Integrated optical/electronic circuits and associated methods of simultaneous generation thereof

ABSTRACT

A method for forming a hybrid active electronic and optical circuit using a lithography mask. The hybrid active electronic and optical circuit comprising an active electronic device and at least one optical device on a Silicon-On-Insulator (SOI) wafer. The SOI wafer including an insulator layer and an upper silicon layer. The upper silicon layer including at least one component of the active electronic device and at least one component of the optical device. The method comprising projecting the lithography mask onto the SOT waver in order to simultaneously pattern the component of the active electronic device and the component of the optical device on the SOI wafer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part to U.S. patent applicationSer. No. 09/859,693, filed May 17, 2001.

This application claims priority to U.S. Provisional Patent ApplicationSerial No. 60/293,615, filed May 25, 2001.

This application claims priority to U.S. Provisional Patent ApplicationSerial No. 60/297,208, filed Jun. 8, 2001.

FIELD OF THE INVENTION

This invention relates to integrated circuits, and more particularly tointegrated circuits including both optical and electronic aspects.

BACKGROUND OF THE INVENTION

In the electronic integrated circuit industry, there is a continuingeffort to increase device speed and increase device densities. Opticalsystems are a technology that promise to increase the speed and currentdensity of integrated circuits. Various components of optical andelectronic integrated circuits can be discrete elements made from glassor clear plastic or alternatively can be formed from a semiconductormaterial, such as silicon.

The majority of the semiconductor industry efforts, including a massivenumber of person-hours of research and development, has focused itsefforts on silicon-based electronic circuits in attempting to makeelectronic circuits faster and more reliable. While other semiconductortechnologies such as Ga—As have shown great promise, the emphasis on theresearch in development in Silicon has reduced the rate of developmentof the other semiconductors. This concentration on silicon devices hasbeen rewarded by quicker and more reliable silicon devices, however therate improvement of silicon-based device speed has decreased in recentyears.

While optical integrated circuits show much promise, there are certaininherent benefits to optical circuits. For instance, at a single level,two electrical conductors cannot be made to cross each other. Bycomparison, one ray of photonic radiation (light) may be made to crossat an angle another ray of photonic radiation without interference therebetween. Light can travel faster between locations that are separated bya great distance than electricity. Fiber-optic systems have thus beenapplied to backbone-type applications such as SONET, that relies on afiber-optic ring technology to provide high bandwidth, high speed datatransfer. Providing frequent conversion between electrical and opticalsignals slows down the data transfer rate and increases the potential oferror in interpreting data levels (differentiating between a digitalhigh and a digital low value). For smaller distance opticalcommunication distances, the benefits of optical communications are notquite as evident and the acceptance of optical systems has been lessthan overwhelming. It is at least years in the future until the opticalindustry appears able to be realize a commercially viable “last mile”connection between the communication backbone or computer networkbackbone and the end user that is necessary for optical systems to befully accepted. Optical computers are even further in the future. Oneuphill battle of optical systems is that electronic systems have beendeveloped so much earlier and are already implemented in many regions.The development of large-scale optical systems have shown.

It would be desirable to provide a variety of silicon-based opticalcircuits to compensate for variations in the operating parameters suchas temperature and device age. In one aspect, it would be very desirableto provide systems that could provide end-user to end-user opticalsignal transfer for communication systems or computer network systems.

SUMMARY OF THE INVENTION

The present invention is directed to a method for forming a hybridactive electronic and optical circuit using a lithography mask. Thehybrid active electronic and optical circuit comprising an activeelectronic device and at least one optical device on aSilicon-On-Insulator (SOI) wafer. The SOI wafer including an insulatorlayer and an upper silicon layer. The upper silicon layer including atleast one component of the active electronic device and at least onecomponent of the optical device. The method comprising projecting thelithography mask onto the SOI waver in order to simultaneously patternthe component of the active electronic device and the component of theoptical device on the SOI wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate the presently preferredembodiment of the invention, and, together with the general descriptiongiven above and the detailed description given below, serve to explainfeatures of the invention.

FIG. 1 shows a front cross sectional view of one embodiment of anoptical waveguide device including a field effect transistor (FET);

FIG. 2 shows a top view of the optical waveguide device shown in FIG. 1;

FIG. 3 shows a section view as taken through sectional lines 3—3 of FIG.2;

FIG. 4 shows a front cross sectional view of one embodiment of anoptical waveguide device including a metal oxide semiconductor capacitor(MOSCAP);

FIG. 5 shows a front view of another embodiment of an optical waveguidedevice including a high electron mobility transistor (HEMT);

FIG. 6 shows a graph plotting surface charge density and the phaseshift, both as a function of the surface potential;

FIG. 7 shows one embodiment of a method to compensate for variations intemperature, or other such parameters, in an optical waveguide device;

FIG. 8 shows another embodiment of a method to compensate for variationsin temperature, or other such parameters, in an optical waveguidedevice;

FIG. 9 shows a top view of another embodiment of optical waveguidedevice 100;

FIG. 10 shows a side cross sectional view of one embodiment of a ridgeoptical channel waveguide device;

FIG. 11 shows a side cross sectional view of one embodiment of a trenchoptical channel waveguide device;

FIG. 12 shows one embodiment of a wave passing though a dielectric slabwaveguide;

FIG. 13 shows a top view of another embodiment of an optical waveguidedevice from that shown in FIG. 2, including one embodiment of a lightcoupler-shaped gate array that provides for light deflection by theoptical circuit;

FIG. 14 shows a top cross sectional view of the waveguide of theembodiment of light coupler-shaped gate array of FIG. 13 includingdotted lines representing a region of changeable propagation constant.The solid light rays are shown passing through the regions of changeablepropagation constant corresponding to the light coupler-shaped gatearray;

FIGS. 15A to 15D show side cross section views of the optical waveguidedevice of FIG. 13 or taken through sectional lines 15—15 in FIG. 13,FIG. 15A shows both gate electrodes 1304, 1306 being deactivated, FIG.15B shows the gate electrode 1304 being actuated as the gate electrode1306 is deactivated, FIG. 15C shows the gate electrode 1304 beingdeactuated as the gate electrode 1306 is activated, and FIG. 15D showsboth gate electrodes 1304 and 1306 being actuated;

FIG. 16 shows a top view of another embodiment of an optical waveguidedevice that is similar in structure to the optical waveguide deviceshown in FIG. 2, with a second voltage source applied from the sourceelectrode to the drain electrode, the gate electrode and electricalinsulator is shown partially broken away to indicate the route of anoptical wave passing through the waveguide that is deflected from itsoriginal path along a variety of paths by application of voltage betweenthe source electrode and gate electrode;

FIG. 17 shows another embodiment of an optical deflector;

FIG. 18 shows a top view of one embodiment of an optical switch thatincludes a plurality of the optical deflectors of the embodiments shownin FIG. 14, 15, or 16;

FIG. 19 shows a top view of another embodiment of an optical switchdevice from that shown in FIG. 18, that may include one embodiment ofthe optical deflectors shown in FIG. 14, 15, or 16;

FIG. 20 shows one embodiment of a grating formed in one of the opticalwaveguide devices shown in FIGS. 1-3 and 5;

FIG. 21 shows another embodiment of a grating formed in one of theoptical waveguide devices shown in FIGS. 1-3 and 5;

FIG. 22 shows yet another embodiment of a grating formed in one of theoptical waveguide devices shown in FIGS. 1-3 and 5;

FIG. 23 shows one embodiment of a waveguide having a grating of the typeshown in FIGS. 20 to 22 showing a light ray passing through the opticalwaveguide device, and the passage of reflected light refracting off thegrating;

FIG. 24 shows an optical waveguide device including a plurality ofgratings of the type shown in FIGS. 20 to 22, where the gratings arearranged in series;

FIG. 25, which is shown expanded in FIG. 25B, shows a respective topview and top expanded view of another embodiment of an optical waveguidedevice including a gate electrode configured that may be configured asan Echelle diffraction grating or an Echelle lens grating;

FIG. 26 shows a top cross sectional view taken within the waveguide ofthe optical waveguide device illustrating the diffraction of opticalpaths as light passes through the actuated Echelle diffraction gratingshown in FIG. 25, wherein the projected outline of the region ofchangeable propagation constant from the Echelle diffraction grating isshown;

FIG. 27 shows an expanded view of the optical waveguide device biased tooperate as an Echelle diffraction grating as shown in FIG. 26;

FIG. 28 shows a top cross sectional view taken through the waveguide ofthe optical waveguide device illustrating the focusing of multipleoptical paths as light passes through the actuated Echelle lens gratingshown in FIG. 25, illustrating the region of changeable propagationconstant resulting from the Echelle lens grating;

FIG. 29 shows an expanded view of the optical waveguide device biased tooperate as an Echelle lens grating as shown in FIG. 28;

FIG. 30 shows a top view of one embodiment of an optical waveguidedevice that includes a grating, and is configured to act as an opticallens;

FIG. 30A shows a top cross sectional view taken through the waveguide ofthe optical waveguide device shown in FIG. 30 illustrating light passingthrough the waveguide;

FIG. 31 shows a top view of another embodiment of optical waveguidedevice that includes a filter grating, and is configured to act as anoptical lens;

FIG. 31A shows a top cross sectional view taken through the waveguide ofthe optical waveguide device shown in FIG. 31 illustrating light passingthrough the waveguide;

FIG. 32 shows a top view of another embodiment of optical waveguidedevice that includes a grating, and is configured to act as an opticallens;

FIG. 32A shows a top cross sectional view taken through the waveguide ofthe optical waveguide device shown in FIG. 32;

FIG. 33 shows a front view of another embodiment of optical waveguidedevice from that shown in FIG. 1;

FIG. 34 shows a top view of one embodiment of an arrayed waveguide (AWG)including a plurality of optical waveguide devices;

FIG. 35 shows a schematic timing diagram of one embodiment of afinite-impulse-response (FIR) filter;

FIG. 36 shows a top view of one embodiment of an FIR filter;

FIG. 37 shows a schematic timing diagram of one embodiment of aninfinite-impulse-response (IIR) filter;

FIG. 38 shows a top view of one embodiment of an IIR filter;

FIG. 39 shows a top view of one embodiment of a dynamic gain equalizerincluding a plurality of optical waveguide devices;

FIG. 40 shows a top view of another embodiment of a dynamic gainequalizer including a plurality of optical waveguide devices;

FIG. 41 shows a top view of one embodiment of a variable opticalattenuator (VOA);

FIG. 42 shows a top view of one embodiment of optical waveguide deviceincluding a channel waveguide being configured as a programmable delaygenerator;

FIG. 43 shows a side cross sectional view of the FIG. 42 embodiment ofprogrammable delay generator;

FIG. 44 shows a top view of one embodiment of an optical resonator thatincludes a plurality of optical waveguide devices that act as opticalmirrors;

FIG. 45 shows a top cross sectional view taken through the waveguide ofthe optical resonator shown in FIG. 44;

FIG. 46 shows a top view of one embodiment of an optical waveguidedevice configured as a beamsplitter;

FIG. 47 shows a top view of one embodiment of a self aligning modulatorincluding a plurality of optical waveguide devices;

FIG. 48 shows a top view of one embodiment of a polarizing controllerincluding one or more programmable delay generators of the type shown inFIGS. 42 and 43;

FIG. 49 shows a top view of one embodiment of an interferometerincluding one or more programmable delay generators of the type shown inFIGS. 42 and 43;

FIG. 50 shows a flow chart of method performed by the polarizationcontroller shown in FIG. 48;

FIG. 51 shows a cross-sectional view of one embodiment of integratedoptical/electronic circuit;

FIG. 52 shows a top view of the embodiment of integratedoptical/electronic circuit of FIG. 51;

FIG. 53 shows a cross-sectional view of one embodiment of integratedoptical/electronic circuit;

FIG. 54 shows a cross-sectional view of another embodiment of integratedoptical/electronic circuit;

FIG. 55 shows yet another cross-sectional view an alternate embodimentof integrated optical/electronic circuit;

FIG. 56 shows a cross-sectional view of yet another alternate embodimentof integrated optical/electronic circuit;

FIG. 57 shows a cross-sectional view of another alternate embodiment ofintegrated optical/electronic circuit;

FIG. 58 shows a cross-sectional view of yet another alternate embodimentof integrated optical/electronic circuit;

FIG. 59 shows an expanded perspective view of an embodiment ofintegrated optical/electronic circuit using flip chip circuits;

FIG. 60 shows a perspective expanded view of an alternate embodiment ofintegrated optical/electronic circuit;

FIG. 61 shows a side cross-sectional view of one embodiment of anoptical/electronic I/O flip chip portion as taken through sectionallines 61/61 of FIG. 60;

FIG. 62 shows another cross-sectional view as taken through across-sectional lines 61—61 of FIG. 60, in accordance with analternative embodiment in which a lower surface is etched;

FIGS. 63A to 63D show a method of fabricating the partially completedintegrated optical/electronic circuit of FIG. 51;

FIG. 64 shows a plot of intensity versus distance from a ledge of oneembodiment of input/output light coupler 112 including a tapered gapportion;

FIG. 65 shows another plot of intensity at a prism base for anotherembodiment of input/output light coupler having a prism, but without atapered gap portion;

FIG. 66 shows one embodiment of hybrid active electronic and opticalcircuit that is configured as a J-coupler;

FIG. 67 illustrates one embodiment of a mask used to anisotropicallyetch regions of a hybrid active electronic and optical circuit;

FIGS. 68A to 68D show one embodiment of a method of anisotropicallyetching using a mask.

FIG. 69 shows a top view of one embodiment of hybrid active electronicand optical circuit that is configured as a two dimensional taper;

FIG. 70 shows a top view of another embodiment of hybrid activeelectronic and optical circuit that is configured as a two dimensionaltaper;

FIG. 71 shows a top view of yet another embodiment of hybrid activeelectronic and optical circuit that is configured as a two dimensionaltaper;

FIG. 72 shows a top view of an embodiment of hybrid active electronicand optical circuit that is configured as an adiabatic taper;

FIG. 73 shows a perspective view of an embodiment of hybrid activeelectronic and optical circuit that is configured as a simpleFabry-Perot cavity;

FIG. 74 shows a perspective view of an embodiment of hybrid activeelectronic and optical circuit that is configured as a coupledFabry-Perot cavity;

FIG. 75 shows a side view of one embodiment of grating similar to asincluded in the simple Fabry-Perot cavity of FIG. 73;

FIG. 76 shows a side view of another embodiment of grating from FIG. 75that is configured as a hybrid active electronic and optical circuit;

FIG. 77 shows a side view of yet another embodiment of grating from FIG.75 that is configured as a hybrid active electronic and optical circuit;

FIG. 78 shows a top view of another embodiment of hybrid activeelectronic and optical circuit that is configured as a wavelengthdivision multiplexer modulator;

FIG. 79 shows a top view of yet another embodiment of hybrid activeelectronic and optical circuit that is configured as a wavelengthdivision multiplexer modulator;

FIG. 80 shows a top view of another embodiment of hybrid activeelectronic and optical circuit in addition to multiple Echelle gratingsand multiple lens that is configured as a wavelength divisionmultiplexer modulator;

FIG. 81 shows a top view of another embodiment of hybrid activeelectronic and optical circuit that is configured as a simple diode; and

FIG. 82 shows a perspective view of one embodiment of prior art photonicband gap device;

FIG. 83 shows a perspective view of one embodiment of a photonic bandgap device;

FIG. 84 shows a top view of one embodiment of optical waveguide device;

FIG. 85 shows a top view of another embodiment of photonic band gapdevice;

FIG. 86 shows a top view of an array of photonic crystals used in aphotonic waveguide device;

FIG. 87 shows a side view of one embodiment of a multi-level photonicwaveguide device;

FIG. 88 shows a side view of another embodiment of a photonic waveguidedevice;

FIG. 89 shows one embodiment of a computer program used to simulateintegrated optical/electronic circuits;

FIG. 90 shows another embodiment of hybrid active electronic opticalcircuit from that shown in FIG. 81; and

FIG. 91 shows another embodiment of hybrid active electronic opticalcircuit from that shown in FIG. 90.

DETAILED DESCRIPTION OF THE EMBODIMENT

The present disclosure describes many aspects of multiple embodiments ofan integrated optical/electronic circuit 103. This disclosure describesto the structural features of the integrated optical/electronic circuit103. Different embodiments of the integrated optical/electronic circuitinclude so-called silicon-on-insulator (SOI) technology, silicon onsapphire, and other technologies. SOI technology has become prevalent inthe electronics industry, and is utilized in such large-productionprocessors as the POWER PC™, and such major companies as IBM andMOTOROLA have devoted considerable research and development resources toSOI. Certain aspects of the integrated optical/electronic circuit 103are described in the “Integrated Optical/Electronic Circuit” portion ofthis disclosure.

Another aspect of this disclosure relates to the optical functionalitythat may be provided by the integrated optical/electronic circuit 103.The integrated optical/electronic circuit 103 includes a plurality ofvaried optical waveguide devices 100 (that may be viewed as opticalbuilding blocks) that together perform the overall opto-electricfunctionality of the integrated optical/electronic circuit 103. Oneembodiment of the optical waveguide devices 100 includes a field effecttransistor (FET) that is arranged to control the light flowingtherethrough to perform the various functions.

The most basic function of one of the optical waveguide devices 100 isto act as an optical modulator. Other optical waveguide devices 100 maybe configured as active or passive optical circuits to perform suchoptical functions as optical deflection, optical filtering, opticalattenuation, optical focusing, optical path length adjustment, variablephase tuning, variable diffraction efficiency, optical coupling, andoptical switching. The structure of the optical waveguide device 103 isdescribed in the “optical waveguide device structure” portion of thisdisclosure. Certain physics aspects of the optical waveguide device isdescribed in the “waveguide physics” portion of this disclosure.

Actual embodiments of discrete optical waveguide devices are describedin the “Specific Embodiments of Optical Waveguide Device” portions ofthis disclosure. More complex optical circuits including a plurality ofoptical waveguide devices 100 are described in the “Optical CircuitsIncluding Optical Waveguide Devices” portion of this disclosure.

Significant aspects of designing any optical waveguide devices 100include being able to couple light from outside of the optical waveguidedevice to inside of the waveguide, and conversely being able to couplelight from the optical waveguide within the optical waveguide device tooutside of the optical waveguide device. If the coupling is poor, thenthe optical waveguide device will be ineffective since the light cannotbe effectively input into, or output from, the waveguide. In usingrelatively thin SOI waveguides, the options of coupling techniques arediminished. Certain embodiments of coupling techniques are disclosed inthe “Input/Output Coupling Embodiments” portion of this disclosure.

Passive optical devices can be made active by the application of anactive electronic circuit applying a voltage to a metallized or highlyconductive, doped semiconductor portion proximate the passive opticalwaveguide, the thereby varying the effective mode index in the waveguideby changing the free-carrier concentration. Such devices and circuitsare described in the hybrid active electronic and optical circuitportion of this disclosure.

Photonic Band Gap Devices are a promising technology by which suchfunctions as modulation, reflection, and diffraction can be performedupon light travelling within a waveguide. Shallow photonic band gapdevices are considered those devices that are formed from photoniccrystals that do not fully extend through the waveguide. Certain aspectsof the photonic band gap device, especially to hybrid active electronicand optical circuit and other integrated optical/electronics circuits,are described in the photonic band gap portion of this disclosure.

I. Integrated Optical/Electric Circuit

FIGS. 51 to 52 show one embodiment of an integrated optical/electriccircuit 103. Multiple embodiments of integrated optical/electric circuit103 are described herein as being formed using SOI devices, etc. Theintegrated optical/electric circuit can be configured with andcombination of active optical, passive optical, active electronics, andpassive components circuit. SOI technology is highly promising forintegrated optical/electronic circuits, and using relatively thin SOIdevices (having an upper silicon layer less than 10μ) has many benefits.Using thin SOI devices for waveguides limits the vertical locations inwhich light can diffract, and therefor acts to localize the light to arelatively narrow waveguide. Thin SOI devices can be formed using planarlithography techniques including deposition and etching processes.

SOI is a commonly-used, heavily researched, and highly acceptedtechnology for electronics using semiconductors. Modifying thealready-accepted SOI platform for optical circuits instead of developingan entirely new technology makes sense. Additionally, it is easier forthe SOI engineers and practitioners to extend the SOI technologycompared to developing, and becoming experienced with, a new technology.Finally, the SOI simulation tools have been refined to such a level thatthe industry trusts the SOI tools. It is easier to modify, and usetrusted output from, the SOI simulation tools than going through theeffort and expense of developing new simulation tools. In case of activedevices, the detailed topology and material profile output from theprocess simulation and free carrier concentration profile output fromthe device simulator is used to predict the optical characteristics ofthe active device.

II. Optical Waveguide Device Structure

There are a variety of optical waveguide devices 100 that are describedin this disclosure in which light travels within, and is containedwithin, a waveguide. Different embodiments of optical waveguide devicesare described that perform different functions to the light contained inthe waveguide. Altering the shape or structure of an electrode(s) canmodify the function of the optical waveguide device 100. Embodiments ofoptical waveguide devices include a waveguide located in a Field EffectTransistor (FET) structure as shown in FIGS. 1 to 3; a waveguideassociated with metal oxide semiconductor capacitor (MOSCAP) structureis shown in FIG. 4; and a waveguide located in the High ElectronMobility Transistor (HEMT) as shown in FIG. 5. In MOSCAPs, one or morebody contact(s) is/are separated from the gate electrode by asemiconductor waveguide and an electrical insulator. MOSCAPS and MOSFETSand other similar structures are understood by the type of dopings incontact with the electrodes; which in turn controls the electricalcharacteristics of the structures. To make the description for the aboveembodiments more uniform, the term “body contact electrodes” is used todescribe either the body contact at the base of the MOSCAP or thesubstantially common potential source electrode and drain electrode inthe FET-like structure.

The application of the voltage between the gate and body contact(s)predominantly changes the distribution of free-carriers (eitherelectrons or holes) near the semiconductor/electrical insulatorboundary. These essentially surface localized changes in the freecarrier distributions are referred to as two-dimensional electron gas or2DEG included in MOSCAPs. In a FET structure, for example, an increasein the application of the bias leads consecutively to accumulation ofcharges (of the same type as the semiconductor i.e. holes in a p-typeand electrons in n-type, depletion, and finally inversion. In 2DEGs, thepolarity of semiconductor is opposite the type of the predominant freecarriers, i.e. electrons in p-type or holes in n-type). In a HighElectron Mobility Transistor (HEMT), the electron (hole) distributionformed just below the surface of the electrical insulator is referred toas 2DEG because of particularly low scattering rates of charge carriers.At any rate, for the purposes of clarity, all of the above shall bereferred to as 2DEG signifying a surface localized charge density changedue to application of an external bias.

The term “semiconductor” is used through this disclosure in particularreference to the waveguides of the particular optical waveguide devices.The semiconductor waveguide is intended to represent a class ofsemiconductor materials. Silicon and Germanium are natural singleelement semiconductors at room temperature. GaAs and InP are examples ofbinary compound semiconductors. There are semiconductors made from threeelement semiconductors such as AlGaAs. The salient feature of allsemiconductors is the existence of a band-gap between the valence andthe conduction band. Multiple layers of semiconductors may also be usedin the construction of a waveguide as well as to create an opticalwaveguide device including a MOSCAP, a FET, or a HEMT. For the purposeof this disclosure, the semiconductor provides the ability to controlthe density of the 2DEG by the application of the gate voltage. Anydescription of a specific semiconductor in this disclosure is intendedto be enabling, exemplary, and not limiting in scope. The conceptsdescribed herein are intended to apply to semiconductors in general.

These concepts relating to the optical waveguide device apply equallywell to any mode of light within a waveguide. Therefore, different modesof light can be modulated using multi-mode waveguides. The physicalphenomena remains as described above for multi-mode waveguides.

The embodiments of optical waveguide device 100 shown in multiplefigures including FIGS. 1-3, and 5, etc. include a field effecttransistor (FET) portion 116 that is electrically coupled to a waveguide106. One embodiment of the waveguide is fabricated proximate to, andunderneath, the gate electrode of the FET portion 116. The waveguide 106is typically made from silicon or another one or plurality of III-Vsemiconductors. The FET portion 116 includes a first body contactelectrode 118, a gate electrode 120, and a second body contact electrode122. A voltage can be applied by e.g., a voltage source 202 to one ofthe electrodes. The gate electrode 120 is the most common electrode inwhich the voltage level is varied to control the optical waveguidedevice. If the first body contact portion 118 and the second bodycontact portion are held at the same voltage by placing an electricalconnector 204 there between, then the optical waveguide device 100operates as a diode. If there is not an electrical connector between thefirst body contact portion 118 and the second body contact portion 122,then the optical waveguide device 100 acts as a transistor. This is truefor each of the following FET/diode configurations. Whether any FEToptical waveguide device 100 is biased to act as a transistor or diode,the optical waveguide device 100 is within the intended scope of thepresent invention since either a diode or a transistor is capable ofaltering the effective mode index in the waveguide as described herein.

The variation in voltage level changes the propagation constant of atleast a portion of the waveguide 106. The changes in the index profileof the waveguide are determined by the location and shapes of all theelectrodes. The density of the 2DEG generally follows the shape of thegate electrode 120. Therefore, the shape of the gate electrode may beconsidered as being projected into a region of changeable propagationconstant 190 (the value of the propagation constant may vary atdifferent locations on the waveguide 106). The region of changeablepropagation constant 190 is considered to be that region through theheight of the waveguide in which the value of the propagation constantis changed by application of voltage to the gate electrode 120. Gateelectrodes 120 are shaped in non-rectangular shapes (as viewed fromabove or the side depending on the embodiment) in the differentembodiments of optical waveguide device. The different embodiments ofthe optical waveguide device perform such differing optical functions asoptical phase/amplitude modulation, optical filtering, opticaldeflection, optical dispersion, etc. Multiple ones of the opticalwaveguide devices can be integrated into a single integratedoptical/electronic circuit as an arrayed waveguide (AWG), a dynamic gainequalizer, and a large variety of integrated optical/electroniccircuits. Such optical waveguide devices and integratedoptical/electronic circuits can be produced using largely existing CMOSand other semiconductor technologies.

FIGS. 1 to 3 will now be described in more detail, and respectively showa front, top, and side view of one embodiment of an optical waveguidedevice 100. FIG. 1 shows a planar semiconductor waveguide bounded bylow-index insulating materials to which the light is coupled using alight coupler 112. Other well-known types of coupling include gratings,tapers, and butt-coupling that are each coupled to the end of thewaveguide. The “gate” electrode 120 is positioned directly above thelight path in the semiconductor waveguide. The gate electrode isseparated from the semiconductor by the low-index dielectric acting asan electrical insulator. The body contact electrodes are electricallycoupled to the semiconductor. This embodiment may be considered to be aFET structure with the body contact electrodes 118, 122 forming asymmetric structure typically referred to as “source” and “drain” in FETterminology. A substantially constant potential conductor 204 equalizesthe voltage level between the first body contact electrode 118 and thesecond body contact electrode 122. The first body contact electrode andthe second body contact electrode can thus be viewed as providingsymmetrical body contact electrodes to the semiconductor. In anotherembodiment, the body contact is placed directly underneath the lightpath and underneath the waveguide.

In yet another embodiment, the body contact is positioned symmetricallylaterally of both sides of, and underneath, the incident light pathwithin the waveguide. The body contact in each of these embodiments isdesigned to change a free-carrier distribution region in a twodimensional electron gas (2DEG) 108 near the semiconductor/electricalinsulator boundary of the waveguide along the light travel path. Thischange in free-carrier distribution results from application of thepotential between the insulated gate electrode and the one or pluralityof body contact electrodes connected to the body of the semiconductor.

The FIG. 1 embodiment shows the optical waveguide device 100 includingan integrated field effect transistor (FET) portion 116. The fieldeffect transistor (FET) portion 116 includes the gate electrode 120, thefirst body contact electrode 118, and the second body contact electrode122, but the channel normally associated with a FET is either replacedby, or considered to be, the waveguide 106. Examples of FETs that can beused in their modified form as FET portions 116 (by using the waveguideinstead of the traditional FET channel) include ametal-oxide-semiconductor FET (MOSFET), a metal-electricalinsulator-semiconductor FET (MISFET), a metal semiconductor FET(MESFET), a modulation doped FET (MODFET), a high electron mobilitytransistor (HEMT), and other similar transistors. In addition, ametal-oxide-silicon capacitor (MOSCAP) may also be similarly modified toform a FET portion.

FIGS. 1, 2, and 3 shows one embodiment of optical waveguide device 100that includes a substrate 102, a first electrical insulator layer 104, awaveguide 106, a first body contact well 107, a second body contact well109, the 2DEG 108, a second electrical insulator layer 110, an inputlight coupler 112, an output light coupler 114, and the field effecttransistor (FET) portion 116. The 2DEG 108 is formed at the junctionbetween the silicon waveguide 106 and the second electrical insulatorlayer 110 of the waveguide 106. Multiple embodiments of opticalwaveguide devices are described that, upon bias of the gate electrode120 relative to the combined first body contact electrode 118 and secondbody contact electrode 122, effect the passage of light through thewaveguide 106 to perform a variety of functions.

The FIG. 12 embodiment of semiconductor waveguide (which may be doped)106 has a thickness h, and is sandwiched between the first electricalinsulator layer 104 and the second electrical insulator layer 110. Thefirst electrical insulator layer 104 and the second electrical insulatorlayer 110 are each typically formed from silicon dioxide (glass) or anyother electrical insulator commonly used in semiconductors, for exampleSiN. The electrical insulator layers 104, 110 confine the light usingtotal internal reflection of the light traversing the waveguide 106.

Light is injected into the waveguide 106 via the input light coupler 112and light exits from the waveguide 106 via the output light coupler 114,although any light-coupling device can be used to respectively inject orremove the light from the waveguide 106. Examples of light-couplingdevices include prisms, gratings, tapers, and butt-couplings. Lightpassing from the input light coupler (or other input port) to the outputlight coupler (or other output port) follows optical path 101 as shownin FIG. 1. The optical path 101 may be defined based upon the functionof the optical waveguide device 100. For example, if the opticalwaveguide device functions as an optical modulator, optical deflector,or an optical filter, the optical path 101 can be respectivelyconsidered to be an optical modulation region, an optical deflectionregion, or an optical filtering region, etc.

As described earlier, application of voltage on the gate electrode 120relative to the combined first body contact electrode 118 and secondbody contact electrode 122 leads to a change in the propagation constantvia changes induced in the free-carrier density distribution 108. In aMOSCAP, the capacitance of the device is controlled by the voltage dueto presence (or absence) of 2DEG. In case of a FET, changes in the freecarrier distribution also control the conductance between the first bodycontact electrode and the second body contact electrode. Thefree-carriers are responsible for changing the optical phase or theamplitude of the guided wave depending on their density which in turn iscontrolled by the gate voltage. The basis of field-effect transistoraction, i.e., rapid change in 2DEG as a function of gate voltage, isalso responsible for the control of the light wave and enablesintegration of electronic and optical functions on the same substrate.Thus traditional FET electronic concepts can be applied to provideactive optical functionality in the optical waveguide device 100. TheFET portion 116 is physically located above, and affixed to, thewaveguide 106 using such semiconductor manufacturing techniques asepitaxial growth, chemical vapor deposition, physical vapor deposition,etc.

The propagation constant (and therefore the effective mode index) of atleast a portion of the waveguide in the optical waveguide device 100 ischanged as the free carrier distribution 108 changes. Such changing ofthe propagation constant results in phase modulation of the lightpassing through that device. The phase modulation occurs in a regions ofchangeable propagation constant, indicated in cross-hatching in FIGS. 1and 3 as 190, that closely follows the two-dimensional planar shape ofthe gate electrode through the height of the waveguide to form a threedimensional shape.

FIG. 2 shows one embodiment of a voltage source configuration thatbiases the voltage of the optical waveguide device 100 by using avoltage source 202 and a substantially constant potential conductor 204.The substantially constant potential conductor 204 acts to tie thevoltage level of the first body contact electrode 118 to the voltagelevel of the second body contact electrode 122. The voltage source 202biases the voltage level of the gate electrode 120 relative to thecombined voltage level of the first body contact electrode 118 and thesecond body contact electrode 122.

To apply a voltage to the gate electrode, a voltage source 202 appliesan AC voltage v_(g) from the gate electrode 120 to the combined firstbody contact electrode 118 and second body contact electrode 122. The ACvoltage v_(g) may be configured either as a substantially regular (e.g.sinusoidal) signal or as an irregular signal such as a digital datatransmission. In one embodiment, the AC voltage v_(g) may be consideredas the information carrying portion of the signal. The voltage source202 can also apply a DC bias V_(g) to the gate electrode 120 relative tothe combined first body contact electrode 118 and second body contactelectrode 122. Depending on the instantaneous value of the V_(g), theconcentration of the 2DEG will accumulate, deplete, or invert as shownby the different regions in FIG. 6. In one embodiment, the DC bias V_(g)is the signal that compensates for changes in device parameters. Thecombined DC bias V_(g) and AC voltage ν_(g) equals the total voltageV_(G) applied to the gate electrode by the voltage source 202. It willbe understood from the description above that modulation of v_(g) canthus be used to effect, for example, a corresponding modulation of lightpassing through the waveguide 106.

The voltage potential of the first body contact electrode 118 is tied tothe voltage potential of the second body contact electrode 122 by thesubstantially constant potential conductor 204. Certain embodiments ofthe substantially constant potential conductor 204 include a meter 205(e.g. a micrometer) to measure the electrical resistance of the gateelectrode from the first body contact electrode to the second bodycontact electrode. The term “substantially” is used when referring tothe constant potential conductor because the meter 205 may generate somerelatively minor current levels in comparison to the operating voltageand current levels applied to the optical waveguide device. The minorcurrent levels are used to measure the resistance of the gate electrode.The current level produced by the meter is relatively small since thevoltage (typically in the microvolt range) of the meter is small, andthe waveguide resistance is considerable (typically in the tens ofohms).

The electrical resistance of the gate electrode is a function of suchparameters as gate voltage, temperature, pressure, device age, anddevice characteristics. As such, the voltage (e.g. the AC voltage or theDC voltage) applied to the gate electrode can be varied to adjust theelectrical resistance of the gate electrode to compensate for suchparameters as temperature, pressure, device age, and/or devicecharacteristics. Therefore, the voltage applied to the gate electrodecan be adjusted to compensate for variations in the operating parametersof the optical waveguide device.

As the temperature of the optical waveguide device varies, the DC biasV_(g) applied to the gate electrode 120 of the optical waveguide deviceis adjusted to compensate for the changed temperature. Other parameters(pressure, device age, device characteristics, etc.) can be compensatedfor in a similar manner as described for temperature (e.g. using apressure sensor to sense variations in pressure). This disclosure is notlimited to discussing the sensing and compensating for temperature sincethe other parameters can be compensated for in a similar manner.Different meter 205 and/or controller 201 embodiments may be provided tocompensate for the different temperatures.

FIG. 7 shows an embodiment of method 700 that compensates fortemperature variations in an optical waveguide device. The method 700starts with step 702 in which the temperature sensor 240 determines thetemperature of the optical waveguide device. The temperature sensor 240can be located either on the substrate or off the substrate. Thetemperature sensor inputs the temperature determined by the temperaturesensor to the controller 201 in step 703. The method 700 continues tostep 704 in which the DC bias V_(g) that is applied to the gateelectrode is adjusted to compensate for variations in the temperature.The controller 201 includes stored information that indicates therequired change in DC bias ΔV_(g) that is necessary to compensate forvariations in temperature, for each value of DC bias V_(g) for eachtemperature within the operating range of the optical waveguide device.The method 700 continues to step 706 in which the AC voltage v_(g) isapplied to operate the optical waveguide device as desired in thewaveguide.

The amount of AC voltage ν_(g) is then superimposed on the DC bias V_(g)that is applied to the gate electrode to provide for the desiredoperation of the optical waveguide device 200 (e.g. the voltagenecessary for optical modulation, optical filtering, optical focusing,etc.). The AC voltage ν_(g) superimposed on the combined DC bias V_(g)and the DC bias change ADC yields the total signal V_(G) applied to thegate electrode.

Another embodiment of compensation circuit, that compensates for thechange in temperature or other operating parameter(s) of the opticalwaveguide device, measures the electrical resistance of the gate betweenthe first body contact electrode 118 and the second body contact 122.The electrical resistance of the waveguide is a function of temperature,device age, device characteristics, and other such parameters. The meter205 measures the electrical resistance of the waveguide. For a givenwaveguide, the same resistance corresponds to the same electron densityand the same hole density in the waveguide. Therefore, if the sameelectrical resistance of the waveguide is maintained, the opticalwaveguide will behave similarly to cause a similar amount of suchoptical action as optical modulation, optical filtering, opticalfocusing, or optical deflection.

FIG. 8 shows another method 800 used by the controller 201 to compensatefor temperature variations of the optical waveguide device. The method800 starts with step 802 in which the meter 205 measures the electricalresistance of the waveguide. The method 800 continues to step 804 inwhich the measured electrical resistance of the waveguide is transferredto the controller 201. The method continues to step 806 in which thecontroller applies the amount of DC bias V_(g) required to be applied tothe gate electrode for that particular value of electrical resistance ofthe waveguide. Such parameters as temperature and device age thattogether may change the electric resistance of the waveguide can thus becompensated for together. Therefore, after measuring the electricalresistance of the waveguide, a feedback loop applies the voltage forthat measured resistance. The method 800 continues to step 808 in whichthe AC voltage v_(g) is applied to operate the optical waveguide device(i.e. modulate, filter, focus, and/or deflect light) as desired in thewaveguide.

In both of these temperature compensating embodiments shown in FIGS. 7and 8, the controller 201 allows the DC bias V_(g) to drift slowly asthe temperature varies to maintain the average resistance of thewaveguide from the source electrode to the drain electrode substantiallyconstant. These temperature-compensating embodiments make the opticalwaveguide device exceedingly stable. As such, the required complexityand the associated expense to maintain the temperature and otherparameters over a wide range of temperatures are reduced considerably.

Suitably changing the voltages applied between the gate electrode 120,and the combined first body contact electrode 118 and second bodycontact electrode 122 results in a corresponding change in the freecarrier distribution in the 2DEG 108. In the FIG. 1 embodiment ofoptical waveguide device 100, altering the voltage applied to the gateelectrode 120 of the FET portion 116 changes the density of freecarriers in the 2DEG 108. Changing free carriers distribution in the2DEG 108 changes the effective mode index of the 2DEG 108 in thewaveguide. Changing the free carrier distribution similarly changes theinstantaneous propagation constant level of the region of changeablepropagation constant 190 (e.g., the area generally underneath the gateelectrode 120 in the FIG. 1 embodiment) within the waveguide 106.

Effective mode index, and equivalently propagation constant, bothmeasure the rate of travel of light at a particular location within thewaveguide taken in the direction parallel to the waveguide. For a lightbeam traveling over some distance in some medium at a velocity V, thevelocity V divided by the speed of light in vacuum is the index for thatmedium. Glass has a propagation constant of 1.5, which means lighttravels 1.5 times slower in glass then it does in a vacuum. For thesilicon in the waveguide the propagation constant is about 3.5. Since aportion of the light path travels in silicon and part of the light pathis in the glass, the propagation constant is some value between 1.5 and3.5. Therefore, the light is travelling at some effective speed measuredin a direction parallel to the axial direction of the waveguide. Thatnumber, or speed, is called effective index of the waveguide. Each modeof light has a distinct effective index (referred to as the effectivemode index) since different modes of the waveguide will effectivelytravel at different speeds.

The effective mode index is the same thing as the propagation constantfor any specific mode of light. The term effective mode index indicatesthat the different modes of light within a waveguide travel at differentvelocities. Therefore there are a plurality of effective indexes for amulti-mode waveguide, each effective index corresponds to a differentmode of light. The propagation constant (or the effective index)measures the average velocity for a phase of light for specific modetravel parallel to the axis of the waveguide as shown in FIG. 12. Thepropagation constant multiplied by the length would indicate how long ittakes to go that length. Through this disclosure, the effective indexfor a mode (the effective mode index) is considered to be the samemeasure as the propagation constant for that mode of light. The termpropagation constant is primarily used throughout the remainder of thedisclosure for uniformity.

Changing the propagation constant of the waveguide 106 by varying the2DEG 108 can phase modulate or amplitude modulate the light in thewaveguide. Within the waveguide, the degree of modulation is local inthat it depends on the density of 2DEG at a particular location. Theshape of the electrode, or other arrangements of body contactelectrodes, can impose a spatially varying phase or amplitude pattern tothe light beam in the waveguide. This in turn can be used to accomplisha wide variety of optical functions such as variable attenuators,optical programmable filters, switches, etc. on the optical signalsflowing through the waveguide 106.

A controller 201 controls the level of the total voltage V_(G) appliedto the voltage source 202. The optical waveguide device 100 can beemployed in a system that is controlled by the controller 201, that ispreferably processor-based. The controller 201 includes a programmablecentral processing unit (CPU) 230 that is operable with a memory 232, aninput/output (I/O) device 234, and such well-known support circuits 236as power supplies, clocks, caches, displays, and the like. The I/Odevice receives, for example, electrical signals corresponding to adesired modulation to be imposed on light passing through the waveguide106. The controller 201 is capable of receiving input from hardware inthe form of temperature sensors and/or meters for monitoring parameterssuch as temperature, optical wavelength, light intensity, devicecharacteristics, pressure, and the like. All of the above elements arecoupled to a control system bus to provide for communication between theother elements in the controller 201 and other external elements.

The memory 232 contains instructions that the CPU 230 executes tofacilitate the monitor and control of the optical waveguide device 100.The instructions in the memory 232 are in the form of program code. Theprogram code may conform to any one of a number of different programminglanguages. For example, the program code can be written in C, C++,BASIC, Pascal, or a number of other languages. Additionally, thecontroller 201 can be fashioned as an application-specific integratedcircuit (ASIC) to provide for quicker controller speed. The controller201 can be attached to the same substrate as the optical waveguidedevice 100.

In the FIG. 1 embodiment of waveguide 106, electrons (hole) concentratein the waveguide to form the 2DEG 108 that forms a very narrow channelnear the boundary of the silicon waveguide 106 and the second electricalinsulator layer 110. The surface inversion charge density q_(n) in the2DEG 108 is a direct function of the local surface potential φ_(s)applied to the waveguide 106. The local surface potential φ_(s) is, inturn, directly related to the total instantaneous voltage on the gateelectrode 120. The total voltage of light in the waveguide V_(G)satisfies the equation V_(G)=V_(g)+ν_(g), where V_(g) is the DC bias andν_(g) is the AC bias. The local surface potential φ_(s) is a function ofthe total voltage V_(G), and is given by the equations: $\begin{matrix}{\phi_{s} = {\frac{Q}{C} + V_{G} + \frac{Q_{OX}}{C_{OX}} + \phi_{ms}}} & 1 \\{\phi_{s} \equiv {\frac{Q}{C} + V_{G}^{\prime}}} & \quad\end{matrix}$

The total potential V_(G) that is applied to the waveguide 106 is thus afactor of the effective capacitance C of the optical waveguide device100. The effective capacitance C itself depends on the distribution ofthe free-carriers. Thus, the capacitance in the MOS like device is afunction of the applied voltage. The charges Q and capacitance C in theequation 1 above are measured per unit area. Since the 2DEG densitydepends only on φ_(s), dopant density, and temperature; 2DEG densityq_(n) can be plotted vs. φ_(s). FIG. 6 illustrates a curve 602 thatplots surface charge density as a function of surface potential for anSi/SiO₂ MOSCAP where the uniform dopant density is assumed to be 10¹⁶cm⁻² at room temperature. FIG. 6 also shows curve 604 that plots phaseshift that is applied to the optical wave passing through waveguide 106for a 3 mm long rectangular gate region. The phase shift is plotted as afunction of surface potential φ_(s).

A side view of one embodiment of the optical waveguide device includinga waveguide located in a MOSCAP is shown in FIG. 4. The opticalwaveguide device includes a MOSCAP 400 including a body contact 402, awaveguide 106, an electric insulator layer 405, and a gate electrode406. In the embodiment of MOSCAP similar to as shown in FIG. 4, avoltage source 410 applies a voltage between the gate electrode 406 andthe body contact 402 to alter a level of propagation constant in aregion of changeable propagation constant 190 within the waveguide 106.The variations to the effective mode index and the propagation constantresult occur similarly to in the FET embodiments of optical waveguidedevice 100 as described below.

In the MOSCAP embodiment of optical waveguide device shown in FIG. 4,the body contact 402 is positioned below the waveguide 106.Alternatively, body contacts may be located where the traditional sourceand drain electrodes exist on traditional FETs. The body contact in theFET embodiment of optical waveguide device shown in FIGS. 1 to 3 isformed from the first body contact electrode being electrically coupledat the same potential as the second body contact electrode. Applicationof the electric field due to the potential difference between the “gate”and the body contacts results in changes in the distribution of freecharges as shown in the embodiment of FIG. 4.

FIG. 5 discloses one embodiment of high electron mobility transistor(HEMT) 500. The HEMT 500 comprises a semi-electric insulating substrate502, an undoped buffer waveguide layer 106, an undoped spacer layer 506,a doped donor layer 508, a 2DEG 505, the first body contact electrode118, the gate electrode 120, and the second body contact electrode 122.In one embodiment, the semi-insulating substrate 502 is formed fromAlGaAs. The undoped buffer waveguide layer 106 is formed from GaAs. Theundoped spacer layer 506 is formed from AlGaAs. The doped donor layer508 is formed from a doped AlGaAs.

During operation of the optical waveguide device, the 2DEG 505 increasesin height (taken vertically in FIG. 5) to approximately 20 angstroms.The 2DEG 505 is generated at the interface between the undoped spacerlayer 506 and the undoped buffer waveguide layer 106 as a result of thenegative biasing of the doped donor layer 508. Such negative biasingdrives the electron carriers in a 2DEG 505 generally downward, therebyforming a p-type 2DEG 505. Application of voltage to the gate electrodetends to increase the free carrier distribution in those portions of the2DEG 505 that are proximate the gate electrode. Such an increase in thefree carrier distribution in the 2DEG increases the effective mode indexin the waveguide 106 formed underneath the 2DEG 505. The gate electrode120 is formed having a prescribed electrode shape. The shape of theeffective mode index region within the waveguide 106 (i.e., the regionhaving an effective mode index that is changed by the application ofvoltage to the gate electrode) generally mirrors the shape of the gateelectrode 120 as viewed from above in FIG. 5. Additionally, the undopedspacer layer 506 acts as an insulative layer, to allow the formation ofthe 2DEG. HEMTs are formed in a variety of embodiments, several of whichare described in U.S. Pat. No. 6,177,685 to Teraguchi et al. that issuedon Jan. 23, 2001 (incorporated herein by reference in its entirety).

From semiconductor physics, the change in the distribution of freecharges is most pronounced near the electrical insulator-semiconductorboundary. These changes in the free-carrier distribution change theindex profile of the optical waveguide from a well-known relationship inplasma physics given by the Drude Model. The change in the free carrierdistribution changes the propagation constant of the optical waveguidedevice from a well-known relationship in plasma physics given by theDrude model in a region of changeable propagation constant 190 withinthe waveguide. The changes in the free-carrier distribution induced inthe semiconductor by the application of electric fields between the gateelectrode and the body contact electrode(s) modulates the phase and/oramplitude of the optical wave passing through the region of changeablepropagation constant 190. Thus, local changes in the free carrierdistribution induced by a change in applied voltage to the gateelectrode are impressed on the local optical phase or the amplitude oflight passing through the waveguide. The shape of the chargedistribution, i.e., the region of changeable propagation constant 190,provides the appropriate optical function as described below. Inmultiple embodiments, the pattern of the gate electrode (i.e., theplanar shape of the gate) controls the shape of the free carrierdistribution. The change in free carrier distribution, in turn, changesthe local effective mode index, or propagation constant, of thewaveguide in the region of changeable propagation constant 190. The samephenomena of change in the refractive index profile of the waveguide maybe ascribed by indicating that group delay or the group velocity of thelight beam has been changed as the free carrier distribution varies.

Therefore, the effective mode index, the propagation constant, the groupdelay, or the group velocity relate to an equivalent concept, namely,parametizing changes in the waveguide's refractive index profile on theoptical beam passing through the region of changeable propagationconstant 190 in the waveguide. This principle applies to all embodimentsof optical waveguide devices, including those shown in FIGS. 1-3, 4, and5.

The relationship between the effective mode index, the propagationconstant, the group delay, or the group velocity apply to waveguides ofall thickness' is now considered. In the case of “thick” waveguides, thelight ray travels by bouncing between the two bounding planes defined bythe insulator layers 110 and 104. The light ray can be easilyidentified, typically using the concept of phase or amplitude changesthat are directly imposed on a beam that has directly undergone one ormultiple interactions with free carriers. However, the concepts ofeffective mode index, propagation constant, group delay, or groupvelocity signify the same final result on the light beam. In thisdisclosure, the terms propagation constant, effective mode index, groupdelay, and group velocity are each used to describe the effects ofchanges in the free-carrier distribution due to electric field appliedto a semiconductor in an optical waveguide device, whether the opticalwaveguide device uses FET, HEMT, MOSCAP, or any other type of opticalwaveguide device technology.

Controlling the 2DEG density provides the optical function of an opticalwaveguide device. As described, adjusting the gate voltage can controlthe 2DEG density. The density may be spatially varied to provide morecomplex functions. A triangular shaped density distribution (included ina region of changeable propagation constant) is capable of deflectingthe light beam in a fashion similar to a prism in ordinary optics. Anundulating pattern of 2DEG of a particular spatial period canreflect/deflect a specific wavelength to form a grating. The exact shapeor the spatial density of the 2DEG is affected by placement of bodycontact electrodes relative to the gate electrode, the shape of the bodycontact electrodes and the gate electrode, and the applied voltagesdiscussed herein. The electric field density between the gate electrodeand the body contact electrode determines the shape of the 2DEG density.The properties or thickness of the insulator can be changed to affectthe density distribution. For example, a grating may be constructed bypatterning the gate electrode as a series of grooves having a constantspacing. In alternate embodiments, the gate electrode can have aconsistent thickness, but the insulator thickness or shape can bealtered to change the electrical resistance between the gate electrodeand the waveguide. All of these embodiments provide an electricallyswitchable grating by controlling the 2DEG density. The 2DEG densitypattern follows the surface potential at the waveguide/electricinsulator boundary rather than the exact shape of the gate electrode.

FIG. 9 shows a top view of another embodiment of optical waveguidedevice 100 that is similar to that shown in the embodiment of FIG. 2,except that the optical waveguide device includes an additional bankgate electrode 902 that is connected to a bank gate electrode well 904.The doping charge of the bank gate electrode well 904 (p++) in oneembodiment is opposite the doping charge (n++) of the source electrodewell and the drain electrode well. During operation, a voltage may beapplied between the bank gate electrode 902 and the connected sourceelectrode and drain electrode to establish a propagation constantgradient formed within the region of changeable propagation constantacross the waveguide from the source electrode to the drain electrode. Avariety of alternative embodiments may be provided to establish apropagation constant gradient formed within the region of changedpropagation constant across the waveguide. For example the width of thesecond electrical insulator layer 110, or the resistance of the materialused in the second electrical insulator layer 110 may be varied toestablish a propagation constant gradient across the waveguide. Sincethere are such a variety of FET, MOSCAP, HEMT, and other configurations,it is envisioned that those configurations are within the intended scopeof optical waveguide device of the present invention.

Optical waveguide devices may be configured either as slab waveguides orchannel waveguides. In channel waveguides, the guided light is bound intwo directions (x and y) and is free to propagate in the axialdirection. In slab waveguides, the guided light is bound in onedirection and can propagate freely in two orthogonal directions. Channelwaveguides are used in such applications as transmission, resonators,modulators, lasers, and certain filters or gratings where the guidedlight is bound in two directions. Slab waveguides are used in suchapplications as deflectors, couplers, demultiplexers, and such filtersor gratings where the guided light is bound only in one direction, andit may be desired to change the direction of propagation.

There are several embodiments of channel waveguides including the FIG.10 embodiment of the ridge channel waveguides 1000 and the FIG. 11embodiment trench channel waveguide 1100. The ridge channel waveguide1000 includes a raised central substrate portion 1002, a electricalinsulator layer 1004, and a metal gate electrode 1005. The raisedsubstrate portion 1002 is n-doped more heavily than the main substrate102. The raised substrate portion 1002 forms a channel defined by a pairof side walls 1006, 1008 on the sides; the electrical insulator layer1004 on the top and the n-doping differential between the raisedsubstrate portion 1002 and the main substrate 102 on the bottom. Thepair of side walls 1006, 1008 includes, or is coated with, a materialhaving a similar index of refraction as the electrical insulator layers104. Biasing the metal gate electrode 1005 forms a 2DEG 108 adjacent theelectrical insulator layer 1004. The 2DEG 108 allows the carriers topass between the first body contact well 107 and the second body contactwell 109 as applied, respectively, by the respective first body contactelectrode 118 and the second body contact electrode 122.

FIG. 11 shows one embodiment of trench channel waveguide 1100. Thetrench channel waveguide includes a plurality of electrical insulativeblocks 1102, 1104 and the waveguide 106. The electrical insulative block1102 partially extends into the waveguide 106 (from the upper surface ofthe optical waveguide device 100) at a lateral location between thefirst body contact well 107 and the gate electrode 120. The electricalinsulative block 1104 partially extends into the waveguide 106 (from theupper surface of the optical waveguide device 100) at a lateral locationbetween the second body contact well 109 and the gate electrode 120. Thelight passing through the waveguide 106 is restrained from travellinglaterally by the addition of the electrical insulative blocks 1102,1104. Spaces 1112, 1114 are defined within the waveguide between eachone of the respective insulative blocks 1102, 1104 and the firstelectrical insulator layer 104. These spaces allow carriers to flowbetween the respective first body contact well 107 and the second bodycontact well 109 through the waveguide 106 formed under the gateelectrode 120.

One embodiment of the optical waveguide devices 100 can be constructedon so-called silicon on insulator (SOI) technology that is used in thesemiconductor electronics field. SOI technology is based on theunderstanding that the vast majority of electronic transistor action inSOI transistors occurs on the top few microns of the silicon. Thesilicon below the top few microns, in principal, could be formed fromsome electrical insulator such as glass. The SOI technology is based onproviding a perfect silicon wafer formed on a layer of an electricalinsulator such as glass (silicon dioxide), that starts two to fivemicrons below the upper surface of the silicon. The electrical insulatorelectrically isolates the upper two to five microns of silicon from therest of the silicon.

The inclusion of the electrical insulator in SOI devices limit the largenumber of electric paths that can be created through a thicker silicon,thereby automatically making SOI transistors go faster and use lesspower consumption. SOI technology has developed over the past decade tobe commercially competitive. For example, Power PC (a registeredtrademark of Apple Computer, Inc. of Cupertino, Calif.) has moved to SOItechnology.

The embodiment of optical waveguide device 100 shown, for example, inFIGS. 1 to 3 may be configured using SOI technology such as processorsand chips. The waveguide 106 of the optical waveguide device 100 may befashioned as the upper SOI silicon layer. The first electrical insulatorlayer 104 may be fashioned as the SOT insulator layer. The substrate 102may be fashioned as the SOI silicon substrate. As such, the SOItechnology including the majority of processors and chips, can easily beused as an optical waveguide device.

III. Waveguide Physics

This section demonstrates that the propagation constant (or equivalentlythe effective mode index) of the waveguide is an instantaneous functionof the 2DEG charge density q_(n). An increase in the free carrierdistribution in a region of the 2DEG 108 results in a correspondingincrease in the propagation constant of the waveguide 106 at thecorresponding region. The relationship between the volumetric density ofthe free carriers and the refractive index was originally derived byDrude in his Model of Metals that indicates that metals provide both adielectric and “free electron” response. The same model may be appliedto semiconductors. The changes in the real part of the refractive indexΔn and the imaginary part of the refractive index Δk (the imaginary partcorresponds to absorption) from an increase in the free carrierdistribution are a function of the change in the free-carrier densityΔN, as indicated by the following equations: $\begin{matrix}{{{\Delta\quad n} = {{\frac{e^{2}}{2ɛ_{0}m_{e}n\quad\omega^{2}}\Delta\quad N} \equiv {{\chi\Delta}\quad N}}}\quad} & 3 \\{{\Delta\quad k} = \frac{\Delta\quad n}{{\omega\tau}_{s}}} & \quad\end{matrix}$

where e is the electronic charge, m_(e) is the effective mass of thecarrier, τ_(s) is the mean scattering time and is related to themobility, and ΔN is the change in the free-carrier density. For thesemiconductor devices considered here, where the dominant change in thefree-carriers is due to the 2DEG, ΔN is a function of q_(n) and thethickness (t) of the 2DEG varies according to the equation:$\begin{matrix}{{\Delta\quad N} = \frac{\Delta\quad q_{n}}{t_{2{DEG}}}} & 4\end{matrix}$

TABLE 1 shows the calculated values of the Drude coefficient χ and theeffective mass m_(e) for Silicon with n or p-type dopants, and GalliumArsinide (GaAs) with n-type doping (at wavelengths of 1.3 and 1.55micron). GaAs and InP both have a larger Drude Coefficient χ thansilicon. This is in part due to the smaller effective mass of charge(electron or hole). Thus, a waveguide structure made from GaAs and InPwill have larger changes in the propagation constant for the samechanges in the density of 2DEG when compared to Silicon.

TABLE 1 Wavelength Material χ m_(e) 1.33 Silicon-n   −7 × 10⁻²² 0.331.55 −9.4 × 10⁻²² 1.33 Silicon-p   −4 × 10⁻²² 0.56 1.55 −5.5 × 10⁻²²1.33 GaAs-n −3.5 × 10⁻²¹ 0.068 1.55 −4.8 × 10⁻²¹

To estimate the length requirements for a dielectric slab waveguide, themodes of the FIG. 12 embodiment of dielectric slab waveguide 106 formedbetween the cladding layers have to satisfy the equation:2k _(y) h+φ ₁+φ₂=2mπ  5

where h is the thickness of the waveguide 106, and the phase shifts φ₁and φ₂ are due to the reflection of the light at the boundary and m isan integer multiple. The propagation constant k_(z) and k_(y) arerelated to k and the mode angle θ by the following equations:k_(y)=k cos θk_(z)=k sin θ, and  6$k = {\left( \frac{2\pi}{\lambda} \right)\quad n}$

Solving equations 5 and 6 can derive the modes of the waveguide 106. Thevalues of φ₁ and φ₂ are functions of angle θ. The change in thepropagation constant k_(z) due to change in the waveguide index profileinduced by the 2DEG is responsible for amplitude and phase modulation.The phase modulation of the light in the waveguide results from a changein the propagation constant of selected regions within the waveguide.The amplitude modulation of the light passing through the waveguideresults from a change in the absorption of the light passing throughselected regions within the waveguide.

The shape and type of the material through which light is passing playsan important role in determining the optical function of the opticalwaveguide device. For example, light passing through a rectangular slaboptical waveguide device only travels axially along the optical path101. Optical deflectors, for example, not only allow the light to travelaxially, but can also deviate the light laterally. The amount ofdisplacement and deviation of the light passing through the waveguideare both dependent on the propagation constant of the waveguide as wellas the apex angle of the light coupler.

The shape of a region of changeable propagation constant 190 within awaveguide plays a role in determining how an application of voltage tothe gate electrode will modify the optical characteristics of lightpassing through the waveguide. For example, a suitably-biasedprism-shaped gate electrode projects a three dimensional prism-shapedregion of changeable propagation constant 190 into the waveguide. Thecross-sectional height of the region of changeable propagation constant190 is projected through the entire height of the waveguide. As viewedfrom above, the region of changeable propagation constant 190 deflectslight in similar propagation directions as light passing through asimilarly shaped optical light coupler. In slab waveguides, the rays oflight will deflect or bounce between the upper and lower surface of thewaveguide while continuing in the same propagation direction as viewedfrom above.

Unlike actual optical circuits that are physically inserted in a path oflight, any effects on light passing through the waveguide of the presentinvention due to the propagation constant within a region of changeablepropagation constant 190 can be adjusted or eliminated by altering thevoltage level applied to the gate electrode. For example, reducing thevoltage applied to a deflector-shaped gate electrode sufficientlyresults in the propagation constant of the projected deflector-shapedregion of changeable propagation constant 190 being reduced to thepropagation constant value of the volume surrounding the region ofchangeable propagation constant 190. In effect, the region of changeablepropagation constant 190 will be removed. Light travelling through theregion of changeable propagation constant 190 will therefore not beeffected by the region of changeable propagation constant 190 within thewaveguide. Similarly, the strength of the propagation constant can bechanged or reversed by varying the voltage applied to the gateelectrode.

IV. Specific Embodiments of Optical Waveguide Devices

A variety of embodiments of optical waveguide devices are now described.Each optical waveguide device shares the basic structure and operationof the embodiments of optical waveguide device described relative toFIGS. 1-3, 4, or 5. The optical waveguide device can be configured ineither the channel waveguide or slab waveguide configuration. Eachembodiment of optical waveguide device is an active device, andtherefore, the voltage level applied to the electrode can control thedegree that the light within the region of changeable propagationconstant 190 in the waveguide will be affected. Since the opticalwaveguide device is active, the propagation constant in the region ofchangeable propagation constant 190 can be adjusted by varying thevoltage applied to the gate electrode. Allowing for such adjustmentusing the controller 201 in combination with either the meter 205 or thetemperature sensor 240 using the methods shown in FIG. 7 or 8 is highlydesirable considering the variation effects that temperature, deviceage, pressure, etc. have on the optical characteristics of the opticalwaveguide device.

The embodiments of optical waveguide device 100 described relative toFIGS. 1 to 3, 4, and 5 can be modified to provide a considerablevariation in its operation. For example, the optical waveguide device100 can have a projected region of changeable propagation constant 190within the waveguide to provide one or more of phase and/or amplitudemodulation, optical deflection, optical filtering, optical attenuation,optical focusing, optical path length adjustment, variable phase tuning,variable diffraction efficiency, optical coupling, etc. As such,embodiments of many optical waveguide devices that perform differentoperations are described in the following sections along with theoperations that they perform.

In each of the following embodiments of an optical waveguide device, thegate electrode is formed in a prescribed electrode shape to perform adesired optical operation. The projected region of changeablepropagation constant 190 assumes a shape similar to, but not necessarilyidentical to, the gate electrode. The shape of the region of changeablepropagation constant 190 within the waveguide can physically mapextremely closely to, with a resolution of down to 10 nm, the prescribedgate electrode shape. The construction and operation of differentembodiments of optical waveguide devices, and the operation, and effectsof various embodiments of regions of changeable propagation constant 190are described in this section.

4A. Optical Modulator

This section describes an optical modulator, one embodiment of opticalwaveguide device 100 that modulates light passing through the waveguide.The embodiments of optical waveguide device as shown in FIGS. 1-3, 4, or5 can perform either phase modulation or amplitude modulation of lightpassing through the waveguide. The modulation of light by the opticalwaveguide device 100 can be optimized by reducing the losses in the gateelectrode 120 as well as reducing the charges in the 2DEG 108, whileincreasing the interaction of the waveguide mode with the 2DEG. Ingeneral, reducing the waveguide thickness h reduces the necessarywaveguide length L_(N) to produce modulation. Limiting the modulation ofthe 2DEG 108 also limits the effects on the free-carriers resulting fromabsorption during modulation. The length required for a specific loss,such as a 10 dB loss L_(10dB), can be experimentally determined for eachdevice. Both L_(N) and L_(10dB) are functions of Δq_(n), Δq_(n) dependson both the DC bias V_(g) as well peak-to-peak variation of the varyingAC signal v_(g).

To construct a high-speed modulator operating with bandwidth in excessof, for example 50 GHz, it is important to consider both the RFmicrowave interfaces and the transit time of the free-carriers. Sincethe carriers arrive in the 2DEG either from the bulk electrode (notshown), from the first body contact electrode 118, or from the secondbody contact electrode 122, as the voltage of the gate electrode 122 ischanged, the time required for the voltage to equilibrate to supply aconstant voltage is, $\begin{matrix}{\tau_{e} = \frac{\left( {L/2} \right)}{v_{s}}} & 7\end{matrix}$

where ν_(s) is the maximum velocity of the carriers and L is the channellength illustrated in FIG. 1. Thus, the maximum length L of the MOS/HEMTstructure of the optical waveguide device 100 is determined by therequirement that τ_(e) be less than some percentage of the bit period.

FIG. 6 shows an illustrative graph of the surface charge density and thephase shift, both plotted as a function of the surface potential for aplanar dielectric waveguide. In the FIG. 6 plot, the waveguide is anexemplary planar Si waveguide that has an electrical insulator layersuch as cladding on both the upper and lower surfaces. The waveguide isa single mode waveguide with the propagation constant of 14.300964 μm⁻¹.A change in the gate voltage by approximately 0.2-0.5 V results in achange to the surface charge density of the 2DEG by 8×10¹² cm⁻² which inturn will lead to a change of −0.01 in the propagation constant if the2DEG was due to electrons. Further assume that this 2DEG region iseffectively confined to within 5-50 nm adjacent the upper electricalinsulator layer, as is typical for MOS device physics. Assuming thatthere is an index change over only a 10 nm distance, the new propagationconstant is calculated to be 14.299792 μm⁻¹. The changes in thepropagation constant result in an additional phase shift of 180 degreesfor light travelling a length of 2.86 mm. Thus, gate voltage modulationleads to phase modulation of light in the waveguide. Similarly,free-carrier absorption occurs in the semiconductor locations wherethere are scattering centers (i.e. donor sites). Such free-carrierabsorption acts to modulate the amplitude of the propagating mode oflight. In general, amplitude modulation and phase shift modulation willoccur simultaneously, but one type of modulation can be arranged to bepredominant by controlling the doping profile of the waveguide.

In one embodiment, a channel waveguide is used to construct a high-speedmodulator. With total internal reflection (TIR) using a channelwaveguide, all the light within the waveguide is constrained to followthe direction parallel to the optical path 101 since the light thatcontacts the electrical insulator layers 104, 110 of the waveguidereflects off the electrical insulator layers. Electrical insulatorlayers 104, 110 have a lower refractive index than the waveguide. Thechannel waveguide should be dimensioned to match the mode(s) of thewaveguide so the waveguide acts as a modulator for that mode.

The first body contact well 107 and the second body contact well 109,that respectively interact with the first body contact electrode 118 andthe second body contact electrode 122, are both typically n-doped. Thisdoping produces the body contact wells 107, 109 having a lowerrefractive index than the silicon waveguide 106 due to the presence offree-carriers. The body contact wells 107, 109 thus form alow-refractive index cladding that naturally confine the light mode(s)laterally within the waveguide 106. The body contact wells 107, 109 alsoabsorb some light passing through the waveguide 106, but the absorptionof light makes the waveguide lossy. Thus, it may be desired to use otherrefractive elements than the electrodes 118, 122 to confine the travelof the optical modes and limit the loss of the light.

For high speed modulation, the body contacts and the gate electrodes canbe made to act like a waveguide that operates at radio frequencies. Itis preferred, depending on the distance required, to produce therequired modulation to match the group velocity of the optical wave tothe microwave.

Variable optical attenuators are one additional embodiment of opticalamplitude modulators. The description of constructing one embodiment ofvariable optical attenuator using optical waveguide devices is describedlater following a description of gratings.

4B. Optical Deflectors

The FIG. 13 embodiment of the optical waveguide device 100 is capable ofacting as an optical deflector 1300 to controllably deflect lightpassing through the waveguide. In one embodiment of deflector 1300, thegate electrode 120 shown in the embodiments of FIGS. 1-3, 4, and 5 isphysically and operationally divided into two electrodes including theinput light coupler gate electrode 1304 and the output light couplergate electrode 1306. Both the input light coupler gate electrode 1304and the output light coupler gate electrode 1306 may be shaped in atrapezoidal or other prismatic) configuration, and are bothsubstantially co-planar and physically positioned above the waveguide.When voltage of a first polarity is applied to one of the input lightcoupler gate electrode 1304 or the output light coupler gate electrode1306 (not simultaneously), light will be deflected from the incidentaxial direction of propagation into opposite lateral directions, e.g.respectively downwardly and upwardly within the waveguide of FIG. 13.When a voltage of one polarity is applied to one of the input lightcoupler gate electrode 1304, light will be deflected in the oppositelateral directions (upward or downward as shown in FIG. 13) as whenvoltage of the same polarity is applied to the output light coupler gateelectrode 1306.

The input light coupler gate electrode 1304 and the output light couplergate electrode 1306 are both formed from an electrically conductivematerial such as metal. A first voltage supply 1320 extends between thecombined first body contact electrode 118 and the input light couplergate electrode 1304. A second voltage supply 1322 extends between thecombined first body contact electrode 118 and second body contactelectrode 122 to the output light coupler gate electrode 1306. The firstvoltage supply 1320 and the second voltage supply 1322 are individuallycontrolled by the controller 201, and therefore an opposite, or thesame, or only one, or neither, polarity voltage can be applied to theinput light coupler gate electrode 1304 and the output light couplergate electrode 1306. The input light coupler gate electrode 1304 and theoutput light coupler gate electrode 1306 can be individually actuated sothat each one of the deflecting prism gate electrodes 1304, 1306 canproject a region of changeable propagation constant 190 in the waveguidewhile the other deflecting prism gate electrode does not. FIGS. 14 and15 (including FIGS. 15A to 15D) show a shape of an embodiment of firstregion of changeable propagation constant 190 a projected by the inputlight coupler gate electrode 1304 closely maps that shape of the inputlight coupler gate electrode shown in FIG. 13. The shape of the FIGS. 14and 15 (including FIGS. 15A to 15D) embodiment of second region ofchangeable propagation constant 190 b projected by the output lightcoupler gate electrode 1306 that closely maps that shape of the outputlight coupler gate electrode 1306 shown in FIG. 13.

The input light coupler gate electrode 1304 has an angled surface 1308whose contour is defined by apex angle 1312. The output light couplergate electrode 1306 has an angled surface 1310 whose contour is definedby apex angle 1314. Increasing the voltage applied to either the inputlight coupler gate electrode 1304 or the output light coupler gateelectrode 1306 increases the free carrier distribution in the region ofthe 2DEG adjacent the respective first region of changeable level ofregion of changeable propagation constant 190 a or the second region ofchangeable propagation constant 190 b of the waveguide, shown in theembodiment of FIG. 15 (that includes FIG. 15A to 15D). Both regions ofchangeable propagation constants 190 a, 190 b are prism (trapezoid)shaped and extend for the entire height of the waveguide and can beviewed as horizontally oriented planar prisms located in the waveguidewhose shape in the plane parallel to the gate electrode is projected bythe respective deflecting prism gate electrodes 1304, 1306. Thewaveguide volume within either one of the regions of changeablepropagation constant 190 a, 190 b has a raised propagation constantcompared to those waveguide regions outside the region of changeablepropagation constant 190 a, 190 b. Additionally, a boundary is formedbetween each one of the regions of changeable propagation constant 190a, 190 b and the remainder of the waveguide. The fact that each one ofthe regions of changeable propagation constant 190 a, 190 b has both araised propagation constant level and a boundary makes the prism-shapedregions of changeable propagation constant 190 a, 190 b act as, andindeed be functionally equivalent to, optical prisms formed of eithersemiconductor material or glass.

As shown in FIG. 15A, when a level of voltage that is insufficient toalter the carrier concentration is applied to either gate electrode 1304and 1306, no 2DEG 108 is established between the electric insulatorlayer 110 and the waveguide 106. Since the 2DEG changes the level ofpropagation constant in the respective regions of propagation constant190 a, 190 b, no regions of changeable propagation constants 190 a or190 b are established in the waveguide 106. Therefore, the propagationconstant of the first region of changeable propagation constant 190 a inthe waveguide matches the propagation constant level of the remainder ofthe waveguide 106, and light travelling along paths 1420, 1422 continuesto follow their incident direction. Path 1420 is shown with a wavefront1440 while path 1422 is shown with a wavefront 1442.

When voltage of a first polarity is applied to the input light couplergate electrode 1304, the first region of changeable propagation constant190 a is projected in the shape of the input light coupler gateelectrode 1304 through the height of the waveguide to form the region ofchanged propagation constant 190 a, as shown in FIG. 15B. The firstregion of changeable propagation constant 190 a thus functions as avariable optical prism that can be selectively turned on and off. Thefirst region of changeable propagation constant 190 a is formed in thesemiconductor waveguide that deflects the light passing along thewaveguide along a path 1430 including wavefronts 1432. Individual beamsof the light following path 1430 are reflected with total internalreflectance between an upper and lower surface of the waveguide, but thedirection of travel of light within the waveguides remains along thepath 1430.

The intensity of the voltage applied to the input light coupler gateelectrode 1304 can be reduced to limit the propagation constant level ofthe region of changed propagation constant, so the light following path1420 would be deflected, e.g., along path 1436 instead of along path1430. The polarity of the voltage applied to the input light couplergate electrode 1304 can also be reversed, and light following path 1420along the waveguide would be deflected to follow path 1438. Therefore,the deflection of the light within the waveguide 106 can be controlled,and even reversed, by controlling the voltage applied to the input lightcoupler gate electrode 1304. Changing of the propagation constant withinthe first region of changeable propagation constant 190 a causes suchdeflection by the input light coupler gate electrode 1304.

When no voltage is applied to the output light coupler gate electrode1306 as shown in FIGS. 15A and 15B, thereby effectively removing thesecond region of changeable propagation constant 190 b from thewaveguide 106. Light following within waveguide 106 along path 1422 isassumed to continue in a direction aligned with the incident light, orin a direction deflected by the input light coupler gate electrode 1304,since the propagation constant is uniform throughout the waveguide.

When voltage of a first polarity is applied to the output light couplergate electrode 1306, the second region of changeable propagationconstant 190 b having a changed propagation constant level is projectedin the waveguide as shown in FIGS. 15C and 15D. The second region ofchangeable propagation constant 190 b may be viewed as an optical prismthat projects in the shape of output light coupler gate electrode 1306to the waveguide, thereby deflecting the light passing along thewaveguide along path 1460 with the wavefronts 1462 extendingperpendicular to the direction of travel.

The intensity of the voltage applied to the output light coupler gateelectrode 1306 shown in FIG. 15C can be reduced, so the light followingpath 1422 would be deflected at a lesser angle, e.g., along path 1466instead of along path 1460. Similarly, increasing the voltage applied tothe output light coupler gate electrode 1306 increases the angle ofdeflection. The polarity of the voltage applied to the output lightcoupler gate electrode 1306 could also be reversed, and light followingpath 1420 within the waveguide would be deflected in a reverseddirection to the original polarity to follow path 1468. Therefore, thedeflection of the light within the waveguide 106 can be controlled, andeven reversed, by controlling the voltage applied to the output lightcoupler gate electrode 1306. Additionally, the propagation constant inprescribed regions of the waveguide, and the gate resistance, can becalibrated using the techniques described in FIGS. 7 and 8 using thecontroller 201, the meter 205, and/or the temperature sensor 240.

The voltage being used to bias the input light coupler gate electrode1304 and/or the output light coupler gate electrode 1306 have the effectof controllably deflecting the light as desired. The FIG. 14 embodimentof optical waveguide device 100 is structurally very similar to theFIGS. 1 to 3 embodiment of optical waveguide device 100, however, thetwo embodiments of optical waveguide devices perform the differingfunctions of modulation and deflection.

In the FIG. 16 embodiment of optical waveguide device, the incidentlight flowing through the waveguide will be deflected from its incidentdirection in a direction that is parallel to the axis of the opticalwaveguide device. Such deflection occurs as result of variable voltageapplied between the second body contact electrode 122 and the first bodycontact electrode 118. In this configuration, an additional voltagesource 1670 applies a voltage between the second body contact electrodeand the first body contact electrode to provide voltage gradient acrossthe gate electrode. By varying the voltage between the second bodycontact electrode and the first body contact electrode, the level ofpropagation constant within the region of changeable propagationconstant changes. The voltage level applied to the waveguide thus causesa direction of the propagation of light flowing through the waveguide tobe controllably changed, leading to deflection of light within thehorizontal plane (e.g. upward and downward along respective paths 1672,1674 as shown in FIG. 16).

The application of the first body contact-to-second body contact voltageV_(SD) 1670 by the voltage source causes a propagation constant gradientto be established across the 2DEG in the waveguide 106 from the firstbody contact electrode to the second body contact electrode. Thus, thepropagation constant, or the effective mode index, of the waveguide 106,varies. This variation in the propagation constant leads to angled phasefronts from one lateral side of the waveguide to another. That is, thewavefront of the optical light flowing through the FIG. 16 embodiment ofwaveguide on one lateral side of the wavefront lags the wavefront on theother lateral side. The phase fronts of the light emerging from the gateregion will thus be tilted and the emerging beam will be deflected by anangle γ. For a fixed V_(DS), the deflection angle γ increases with thedistance z traveled within the waveguide. The angle γ can be calculatedby referring to FIG. 16 according to the equation. $\begin{matrix}{\gamma = {{a\quad{\tan\left( \frac{\Delta\quad{OP}}{L} \right)}} = {{a\quad{\tan\left( \frac{\Delta\overset{\_}{n}W}{L} \right)}} = {a\quad{\tan\left( \frac{\overset{\_}{n}{\cot(\theta)}{\Delta\theta}\quad W}{L} \right)}}}}} & 8 \\{{\therefore\gamma} = {\left( \frac{W}{L} \right)10^{- 4}}} & \quad\end{matrix}$

Another embodiment of optical deflector 1700 is shown in FIG. 17. Thewaveguide 1702 is trapezoidal in shape. A gate electrode 1706 (that isshown as hatched to indicate that the gate electrode shares the shape ofthe waveguide 1702 in this embodiment) may, or may not, approximate thetrapezoidal shape of the waveguide. Providing a trapezoidal shapedwaveguide in addition to the shaped gate electrode enhances thedeflection characteristics of the optical deflector on light. In theoptical deflector 1700, if the voltage applied to the gate electrode isremoved, deflection occurs due to the shape of the waveguide due to thetrapezoidal shape of the waveguide. In this embodiment of opticalwaveguide device, the waveguide itself may be shaped similarly to theprior-art discrete optical prisms formed from glass.

FIG. 18 shows one embodiment of optical switch 1800 including aplurality of optical deflectors that each switches its input light fromone or more deflecting prism gate electrodes 1802 a through 1802 e toone of a plurality of receiver waveguides 1808 a to 1808 e. The opticalswitch 1800 includes an input switch portion 1802 and an output switchportion 1804. The input switch portion includes a plurality of the FIG.18 embodiment of deflecting prism gate electrodes as 1802 a to 1802 e.The deflecting prism gate electrodes 1802 a to 1802 e may each beconstructed, and operate, as described relative to one of the deflectingprism gate electrodes 1306, 1304 of FIG. 13. Each one of the deflectingprism gate electrodes 1802 a to 1802 e is optically connected at itsinput to receive light signals from a separate channel waveguide, notshown in FIG. 18. The output portion 1806 includes a plurality ofreceiver waveguides 1808 a, 1808 b, 1808 c, 1808 d, and 1808 e. Each ofthe receiver waveguides 1808 a to 1808 e is configured to receive lightthat is transmitted by each of the deflecting prism gate electrodes 1802a to 1802 e.

The optical switch 1800 therefore includes five deflecting prism gateelectrodes 1802 a to 1802 e, in addition to five receiver waveguides1808 a to 1808 e. As such, the optical switch can operate as, e.g., a5×5 switch in which any of the deflecting prism gate electrodes 1802 ato 1802 e can deflect its output light signal to any, or none, of thereceiver waveguides 1808 a to 1808 e. Each of the deflecting prism gateelectrodes 1802 a to 1802 e includes a gate portion that is configuredwith a respective angled apex surface 1810 a to 1810 e. Voltage suppliedto any of the deflecting prism gate electrodes 1802 a to 1802 e resultsin an increase in the propagation constant within the correspondingregion of changeable propagation constant 190 (that forms in thewaveguide below the corresponding deflecting prism gate electrode 1802 ato 1802 e shown in FIG. 18) associated with that particular deflectingprism's gate electrode.

Although the FIG. 18 embodiment of waveguide operates similarly to theFIG. 15 embodiment of waveguide, if no voltage is applied to anyparticular deflecting prism gate electrode 1802 a to 1802 e, then thelight travels directly through the waveguide associated with thatdeflecting prism gate electrode and substantially straight to arespective receiver waveguide 1808 a to 1808 e located in front of thatdeflecting prism gate electrode. The apex angles 1810 a and 1810 e(and/or the angles of the waveguide as shown in the FIG. 17 embodiment)of the outer most deflecting prism gate electrodes 1802 a and 1802 e areangled at a greater angle than deflecting prism gate electrodes 1802 b,1802 c, and 1802 d. An increase in the apex angle 1810 a and 1810 eallows light flowing through the waveguide to be deflected through agreater angle toward the more distant receivers 1808 a to 1808 e. It mayalso be desired to minimize the lateral spacing between each successivedeflecting prism gate electrode 1802 a to 1802 e, and the lateralspacing between each respective receiver 1808 a to 1808 e to minimizethe necessary deflection angle for the deflecting prism gate electrodes.The apex angle of those deflecting prism gate electrodes that aregenerally to the left of an axial centerline of the optical switch (andthus have to deflect their light to the right in most distances) areangled oppositely to the apex angle of those deflecting prism gateelectrodes that are to the right of the centerline of that switch thathave to deflect their light to the left in most instances. Deflectingprism gate electrodes 1802 b, 1802 c, and 1802 d that have otherdeflecting prism gate electrodes locate to both their right and leftshould also have receivers located both to their right and left as shownin FIG. 18 and therefore must be adapted to provide for deflection oflight to either the left or right. For example, the deflecting prismgate electrode 1802 c must cause light traveling through its waveguideto be deflected to the right when transmitting its signal to thereceivers 1808 d or 1808 e. By comparison, the deflecting prism gateelectrode 1802 c must cause light that is passing through its waveguideto be deflected to its left when deflecting light to receivers 1808 aand 1808 b.

Optical switch 1800 has the ability to act extremely quickly, partly dueto the fact that each deflecting prism gate electrode has no movingparts. Each of the deflecting prism gate electrodes 1802 a to 1802 e canbe adjusted and/or calibrated by controlling the voltage applied to thatdeflecting prism gate electrode using the techniques described in FIGS.7 and 8. Applying the voltage to the deflecting prism gate electrodes1802 a to 1802 e results in an increase, or decrease (depending onpolarity), of the propagation constant level of the region of changeablepropagation constant in the waveguide associated with that deflectingprism gate electrode 1802 a to 1802 e.

FIG. 19 shows another embodiment of optical switch 1900. The opticalswitch includes a concave input switch portion 1902 and a concave outputswitch portion 1904. The input switch portion 1902 includes a pluralityof deflecting prism gate electrodes 1902 a to 1902 d (having respectiveapex angles 1910 a to 1910 d) that operate similarly to the FIG. 18embodiment of deflecting prism gate electrodes 1802 a to 1802 e.Similarly, the concave output switch portion 1902 includes a pluralityof receivers 1908 a to 1908 d. Each one of the receivers 1908 a to 1908d operates similarly to the FIG. 18 embodiment of receivers 1808 a to1808 e. The purpose of the concavity of the concave input switchdeflector portion 1902 and the concave output portion 1904 is tominimize the maximum angle through which any one of the opticaldeflecting prism gate electrodes has to deflect light to reach any oneof the receivers. This is accomplished by mounting each of the opticaldeflecting prism gate electrodes at an angle that bisects the raysextending to the outermost receivers 1908 a to 1908 d. The mounting ofthe optical deflecting gate electrodes also generally enhances thereception of light by the receivers since each receiver is directed atan angle that more closely faces the respective outermost opticaldeflecting prism gate electrodes. The operation of the embodiment ofoptical switch 1900 in FIG. 19 relative to the deflecting prism gateelectrodes 1902 a to 1902 d and the receivers 1908 a and 1908 d issimilar to the above-described operation of the optical switch 1800 inFIG. 18 relative to the respective deflecting prism gate electrodes 1802a to 1808 e (except for the angle of deflection of the deflecting prismgate electrode).

4C. Optical Gratings

Gratings in the dielectric slab waveguide as well as in fibers are wellknown to perform various optical functions such as optical filtering,group velocity dispersion control, attenuation, etc. The fundamentalprinciple behind grating is that small, periodic variation in the modeindex or the propagation constant leads to resonant condition fordiffraction of certain wavelengths.

These wavelengths satisfy the resonant condition for build up ofdiffracted power along a certain direction. The wavelength selectivitydepends on the design of the grating structure. In the case presentedhere, we envision a grating that is electrically controlled via theeffect of 2DEG. There are many ways to produce the undulating pattern in2DEG. The methods include: undulation in the effective dielectricconstant of the gate insulator, patterned gate metal, periodic dopingmodulation etc. FIG. 20 is one example. In FIG. 20 the gate dielectricis divided into two gate insulators of different dielectric strength.

FIGS. 20 to 22 show a variety of embodiments of optical gratings inwhich the shape or configuration of the gate electrode 120 of theoptical waveguide device 106 is slightly modified. Gratings perform avariety of functions in optical systems involving controllable opticalrefraction as described below. In the different embodiments of opticalgratings, a series of planes of controllable propagation constant(compared to the surrounding volume within the waveguide) are projectedinto the waveguide 106. The planes of controllable propagation constantmay be considered to form one embodiment of a region of changeablepropagation constant 190, similar to those shown and described relativeto FIGS. 1-3, 4, or 5. In the FIG. 20 embodiment of optical grating2000, the second insulator layer 110 is provided with a corrugated lowersurface 2002. The corrugated lower surface includes a plurality ofraised lands 2004 that provide a variable thickness of the secondinsulator layer 110 between different portions of the corrugated lowersurface of the second electrical insulator layer or oxide 110 and thegate electrode 120. Each pair of adjacent raised lands 2004 areuniformly spaced for one grating.

A distance T1 represents the distance between the raised lands 2004 ofthe corrugated surface 2002 and the gate electrode 120. A distance T2represents the distance from the lower most surface of the corrugatedsurface 2002 and the gate electrode 120. Since the distance T1 does notequal T2, the electrical field at the insulator/semiconductor interfaceof the second insulator layer 110 from the gate electrode to thewaveguide 106 will vary along the length of the waveguide. For example,a point 2006 in the waveguide that is underneath the location of one ofthe raised lands 2004 experiences less electrical field at theinsulator/semiconductor interface to voltage applied between the gateelectrode and the waveguide than point 2008 that is not underneath thelocation of one of the raised lands. Since the resistance of the secondinsulator layer 110 in the vertical direction varies along its length,the resistance between the gate electrode and the waveguide (that hasthe second insulating layer interspersed there between) varies along itslength. The strength of the electrical field applied from the gateelectrode into the waveguide varies as a function of the thickness ofthe second insulator layer 110. For example, the projected electricalfield within the waveguide at point 2006 exceeds the projected electricfield at point 2008. As such, the resultant free carrier chargedistribution in the 2DEG above point 2006 exceeds the resultant freecarrier charge distribution in the 2DEG above point 2008. Therefore, theresultant propagation constant in the projected region of changeablepropagation constant 190 in the waveguide at point 2006 exceeds theresultant propagation constant in the projected region of changeablepropagation constant 190 in the waveguide at point 2008.

The raised lands 2004 are typically formed as grooves in the secondinsulator layer 110 that extend substantially perpendicular to, orangled relative to, the direction of light propagation within thewaveguide. The raised lands 2004 may extend at a slight angle asdescribed with respect to FIG. 23 so that reflected light passingthrough the waveguide may be deflected at an angle to, e.g., anotherdevice. A low insulative material 2010 is disposed between the secondelectrical insulator layer 110 and waveguide 106. The previouslydescribed embodiments of optical waveguide devices relied on changes inthe planar shape of the gate electrode to produce a variable region ofchangeable propagation constant 190 across the waveguide. The FIGS. 20to 22 embodiments of optical waveguide devices rely on variations ofthickness (or variation of the electrical resistivity of the material)of the gate electrode, or the use of an insulator under the gateelectrode, to produce a variable propagation constant across thewaveguide.

Since a variable electromagnetic field is applied from the gateelectrode 120 through the second electrical insulator layer or oxide 110to the waveguide 106, the propagation constant of the waveguide 106 willvary. The carrier density in the 2DEG 108 will vary between the locationin the 2DEG above the point 2006 and above the point 2008. Moreparticularly, the lower resistance of the second electrical insulatorlayer or oxide at point 2006 that corresponds to distance T1 will resultin an increased carrier density compared to the point 2008 on the 2DEGthat corresponds to an enhanced distant T2, and resulting in anincreased resistance of the 2DEG. Such variation in the propagationconstant along the length of the waveguide 106 results only when gateelectrode 120 is actuated. When the gate electrode is deactuated, thepropagation constant across the waveguide 106 is substantially uniform.In the FIGS. 20 to 22 embodiments of optical gratings, the propagationconstant is changed by the thickness of the gate electrode, i.e., theraised lands locations. Therefore, this embodiment of optical waveguidedevice changes the propagation constant by changing the thickness of thegate electrode to form the gratings, not by changing the shape of thegate electrode.

Such a variation in propagation constant within certain regions at thewaveguide 106 will result in some percentage of the light travelingalong the waveguide 106 to be reflected. The variation in thepropagation constant extends substantially continuously across thelength of the FIG. 20 embodiment of waveguide 106. As such, even thougha relatively small amount of energy of each light wave following adirection of light travel 101 will be reflected by each plane projectedby a single recess, a variable amount of light can be controllablyreflected by the total number of planes 2012 in each grating. Thedistance d in the direction of propagation of light between successiveplanes within the grating is selected so that the light waves reflectedfrom planes 2012 are in phase, or coherent, with the light reflectedfrom the adjacent planes. The strength of the 2DEG determines thereflectivity or the diffraction efficiency of the grating structure. Byvarying the strength, we may chose to control the light diffracted bythe grating structure. This will be useful in construction of theattenuators, modulators, switches etc.

The light waves travelling in direction 101 from the adjacent phaseplanes 2012 will be in phase, or coherent, for a desired light ofwavelength λ if the difference in distance between light reflected fromsuccessive planes 2012 equals an integer multiple of the wavelength ofthe selected light. For example, light traveling along the waveguide 106(in a direction from left to right as indicated by the arrow inwaveguide 106) that is reflected at the first plane 2012 (the planefarthest to the left in FIG. 20) is reflected either along the waveguide106 or at some angle at which the reflected light beam is deflected, andtravels some distance shorter than light reflected off the next plane(the first plane to the right of the leftmost plane 2012 in FIG. 20).

Light reflected from the gratings of the waveguide will be in-phase, orcoherent, when the distance d between recesses taken in a directionparallel to the original direction of propagation of the light in thewaveguide is an integer multiple of a selected bandwidth of light. Inthe FIG. 23 embodiment of grating, light reflected off successive planes2311 would coherently add where the distance “d” is some integermultiple of the wavelength of the reflected light. The other wavelengthsof light interfere destructively, and cannot be detected by a detector.

The FIG. 21 embodiment of grating 2100 includes a plurality ofinsulators 2102 evenly spaced between the electrical insulator layer 110and the waveguide 106. The electrical resistance of the insulators 2102differs from that of the electrical insulator layer 110. Alternatively,inserts could be inserted having a different electrical resistance thanthe remainder of the electrical insulator layer.

The insulator 2102 limits the number of carriers that are generated inthose portions of the 2DEG 108 below the insulators 2102 compared tothose locations in the 2DEG that are not below the insulators 2102. Assuch, the propagation constant in those portions of the waveguide 106that are below the insulators 2102 will be different than thepropagation constant in those portions of the waveguide that are notbelow the insulators 2102. Planes 2112 that correspond to the regions ofchanged propagation constant within the waveguide under the insulatorsthat are projected into the waveguide 106. Such planes 2112 aretherefore regularly spaced since the location of the projected regionsof changeable propagation constant corresponds directly to the locationof the insulators 2102. The insulator properties that control thestrength of the electric field at the insulator/semiconductor interfaceare due to its dielectric constant at the modulation frequencies ofinterest. The insulator may have variable dielectric constant at radiofrequencies but is substantially unchanged at the optical frequencies.Thus, optical wave does not “see” the undulation unless induced by 2DEG.

In the FIG. 22 embodiment of optical grating 2200, another shape ofregularly shaped patterning, that may take the form of corrugatedpatterns along the bottom surface of the gate electrode 120, is formedin the gate electrode 120. The optical grating 2200 includes a series ofraised lands 2202 formed in the lower surface the of the metal gateelectrode 120. These raised lands 2202 may be angled relative to thewaveguide for a desired distance. The raised lands 2202 in the gateelectrode are configured to vary the electrical field at theinsulator/semiconductor interface to the waveguide 106 in a patterncorresponding to the arrangement of the raised lands 2202. For example,the propagation constant will be slightly less in those regions of thewaveguide underneath the raised lands 2202 than in adjacent regions ofthe waveguide since the distance that the raised lands 2202 areseparated from the waveguide is greater than the surrounding regions.

In this disclosure, gratings may also be configured using a SAW, or anyother similar acoustic or other structure that is configured to projecta series of parallel planes 2112 representing regions of changeablepropagation constant into the waveguide 106.

The planes 2311 are each angled at an angle α from the direction ofpropagation of the incident light 2304. As such, a certain amount oflight is reflected at each of the planes 2311, resulting in reflectedlight 2306. The majority of light 2304 continues straight through thewaveguide past each plane 2311, with only a relatively minor portionbeing reflected off each plane to form the reflected light 2306. Thedifference in distance traveled by each successive plane 2311 thatreflects light is indicated, in FIG. 23, by the distance d measured in adirection parallel to the incident light beam 2304. Therefore, distanced is selected to be some multiple of the wavelength of the light that isto be reflected from the FIG. 23 embodiment of optical grating. Theselected wavelength X of light that reflects off successive planesspaced by the distance d must satisfy the equation:

 2 sin α=λ/d  9

If each reflected light path 2306 distance varies by an integer multipleof the wavelength of the selected light, the light at that selectedwavelength will constructively interfere at a detector 2312 and thus bevisible. The detector can be any known type of photodetector. Since thedistance d has been selected at a prescribed value, the distance of eachray of reflected light 2306 off each plane travels a slightly greaterdistance than a corresponding ray of light reflected off the precedingplane (the preceding plane is the plane to the left as shown in FIG.23). Those wavelengths of light that are not integer multiples of thedistance d, will interfere destructively and thus not be able to besensed by the detector 2312.

The gratings represent one embodiment of a one-dimensional periodicstructure. More complicated optical functions may be achieved by using atwo dimensional periodic patterns. One embodiment of a two-dimensionalperiodic structure that corresponds to the grating includes using a“polka dot” pattern, in which the reflectivity of a particular group ofwavelengths are unity in all directions in the plane. A “line defect” inthe pattern may be provided that results in the effective removal of oneor more of these “polka dots” along a line in a manner that causesguiding of light along the line defect. Many geometrical shapes can beused in addition to circles that form the polka dot pattern. All ofthese can be achieved by generalization of the gratings discussed indetail above to the one-dimensional patterns.

FIG. 23 shows one embodiment of optical grating 2303 that is configuredto diffract light. A series of such optical gratings labeled as 2303 ato 2303 e can be applied to the FIG. 24 embodiment of waveguide. Thespecific optical grating 2303 relating to a desired wavelength λ oflight can be actuated, while the remainder of the optical gratings 2303are deactuated. One design may provide a plurality of optical gratings2303 arranged serially along a channel waveguide, with only a minimaldifference between the wavelengths λ of the reflected light bysuccessive optical gratings 2303 a to 2303 e. For example, the firstoptical grating 2303 a reflects light having a wavelength λ₁ thatexceeds the wavelength λ₂ of the light that is diffracted by the secondoptical grating 2303 b. Similarly, the wavelength of light that can bereflected by each optical grating is greater than the wavelength thatcan be reflected by subsequent gratings. To compensate for physicalvariations in the waveguide (resulting from variations in temperature,device age, humidity, or vibrations, etc.), a grating that correspondsto a desired wavelength of reflected light may be actuated, and then thereflected light monitored as per wavelength. If multiple opticalgratings are provided to allow for adjustment or calibration purposes,then the differences in spacing between successive planes of thedifferent optical gratings is initially selected. If it is found thatthe actuated grating does not deflect the desired light (the wavelengthof the deflected light being too large or too small), then anotheroptical grating (with the next smaller or larger plane spacing) can thenbe actuated. The selection of the next grating to actuate depends uponwhether the desired wavelength of the first actuated optical grating ismore or less than the wavelength of the diffracted light. Thisadjustment or calibration process can be performed either manually or bya computer using a comparison program, and can be performed continuallyduring normal operation of an optical system employing optical gratings.

FIG. 25 shows one embodiment of Echelle grating 2500. The Echellegrating 2500 may be used alternatively as a diffraction grating or alens grating depending on the biasing of the gate electrode. The Echellegrating 2500 is altered from the FIGS. 1 to 3 and 5 embodiment ofoptical waveguide device 100 by replacing the rectangular gate electrodeby a triangular-shaped Echelle gate electrode 2502. The Echelle-shapedgate electrode 2502 includes two parallel sides 2504 and 2506 (side 2506is shown as the point of the triangle, but actually is formed from alength of material shown in FIG. 26 as 2506), a base side 2510, and aplanar grooved surface 2512.

The base surface 2510 extends substantially perpendicular to theincident direction of travel of light (the light is indicated by arrows2606, 2607, and 2609 shown in FIG. 26) entering the Echelle grating. Asshown in FIG. 25B, the grooved side 2512 is made of a series ofindividual grooves 2515 that extend parallel to the side surface, andall of the grooves regularly continue from side 2504 to the other side2506. Each groove 2515 includes a width portion 2519 and rise portion2517.

The rise portion 2517 defines the difference in distance that eachindividual groove rises from its neighbor groove. The rise portion 2517for all of the individual grooves 2515 are equal, and the rise portion2517 equals some integer multiple of the wavelength of the light that isto be acted upon by the Echelle grating 2500. Two exemplary adjacentgrooves are shown as 2515 a and 2515 b, so the vertical distance betweenthe grooves 2515 a and 2515 b equals 2517. The width portion 2519 of theEchelle shape gate electrode 2502 is equal for all of the individualgrooves. As such, the distance of the width portion 2519 multiplied bythe number of individual grooves 2515 equals the operational width ofthe entire Echelle shaped gate electrode. Commercially available threedimensional Echelle gratings that are formed from glass or asemiconductor material have a uniform cross section that is similar incontour to the Echelle shaped gate electrode 2502. The projected regionof changeable propagation constant 190 can be viewed generally incross-section as having the shape and dimensions of the gate electrode(including grooves), and extending vertically through the entirethickness of the waveguide 106. The numbers of individual grooves 2515in the FIG. 25 embodiment of Echelle shaped gate electrode 2502 mayapproach many thousand, and therefore, the size may become relativelysmall to provide effective focusing.

FIG. 26 shows the top cross sectional view of region of changeablepropagation constant 190 shaped as an Echelle grating 2500. Thewaveguide 106 is envisioned to be a slab waveguide, and is configured topermit the angular diffraction of the beam of light emanating from theEchelle grating 2500. When voltages are applied to the FIG. 25embodiment of Echelle shaped gate electrode 2502, a projected region ofchangeable propagation constant 190 of the general shape shown in FIG.26 is established within the waveguide 106. Depending upon the polarityof the applied voltage to the Echelle shaped gate electrode in FIG. 25,the propagation constant within the projected region of changeablepropagation constant 190 can either exceed, or be less than, thepropagation constant within the waveguide outside of the projectedregion of changeable propagation constant 190. The relative level ofpropagation constants within the projected region of changeablepropagation constant 190 compared to outside of the projected region ofchangeable propagation constant determines whether the waveguide 106acts to diffract light or focus light. In this section, it is assumedthat the voltage applied to the gate electrode is biased so the Echellegrating acts to diffract light, although equivalent techniques wouldapply for focusing light, and are considered a part of this disclosure.

In FIG. 26, three input light beams 2606, 2607, and 2609 extend into thewaveguide. The input light beams 2606, 2607, and 2609 are shown asextending substantially parallel to each other, and also substantiallyparallel to the side surface 2520 of the projected region of changeablepropagation constant 190. The projected region of changeable propagationconstant 190 as shown in FIG. 26 precisely mirrors the shape and size ofthe FIG. 25 embodiment of Echelle shaped gate electrode 2502. As such,the projected region of changeable propagation constant 190 can beviewed as extending vertically through the entire thickness of thewaveguide 106. The numbers of individual grooves 2515 in the FIG. 25embodiment of Echelle shaped gate electrode 2502 may approach manythousand to provide effective diffraction, and therefore, individualgroove dimensions are relatively small. It is therefore important thatthe projected region of changeable propagation constant 190 preciselymaps from the Echelle shaped gate electrode 2502.

Three input beams in 2606, 2607, and 2609 are shown entering theprojected region of changeable propagation constant 190, each containingmultiple wavelengths of light. The three input beams 2606, 2607, and2609 correspond respectively with, and produce, three sets of outputbeams 2610 a or 2610 b; 2612 a, 2612 b or 2612 c; and 2614 a or 2614 bas shown in FIG. 26. Each diffracted output beam 2610, 2612, and 2614 isshown for a single wavelength of light, and the output beam representsthe regions in which light of a specific wavelength that emanates fromdifferent grooves 2604 will constructively interfere. In otherdirections, the light destructively interferes.

The lower input light beam 2606 that enters the projected region ofchangeable propagation constant 190 travels for a very short distance d1through the projected region of changeable propagation constant 190(from the left to the right) and exits as output beam 2610 a or 2610 b.As such, though the region of changeable propagation constant 190 has adifferent propagation constant then the rest of the waveguide 106, theamount that the output beam 2610 a, or 2610 b is diffracted is verysmall when compared to the amount of diffraction of the other outputbeams 2612, 2614 that have traveled a greater distance through theprojected region of changeable propagation constant 190.

The middle input light beam 2607 enters the projected region ofchangeable propagation constant 190 and travels through a considerabledistance d2 before exiting from the Echelle grating. If there is novoltage applied to the gate electrode, then the output light will beunaffected by the region of changeable propagation constant 190 as thelight travels the region, and the direction of propagation for lightfollowing input path 2607 will be consistent within the waveguide along2612 a. If a voltage level is applied to the FIG. 25 embodiment of gateelectrode 2502, then the propagation constant within the region ofchangeable propagation constant 190 is changed from that outside theregion of changeable propagation constant. The propagation constant inthe region of changeable propagation constant 190 will thereupondiffract light passing from the input light beam 2607 through an angleθ_(d1) along path 2612 b. If the voltage is increased, the amount ofdiffraction is also increased to along the path shown at 2612 c.

Light corresponding to the input light beam 2609 will continue instraight along line 2614 a when no voltage is applied to the gateelectrode. If a prescribed level of voltage is applied to the gateelectrode, the output light beam will be diffracted through an outputangle θ_(d2) along output light beam 2614 b. The output angle θ_(d2) ofoutput diffracted beam 2614 b exceeds the output angle θ_(d1) ofdiffracted beam 2612 b. The output angle varies linearly from one sidesurface 2522 to the other side surface 2520, since the output angle is afunction of the distance the light is travelling through the projectedregion of changeable propagation constant 190.

When the Echelle grating diffracts a single wavelength of light throughan angle in which the waves are in phase, the waves of that lightconstructively interfere and that wavelength of light will becomevisible at that location. Light of a different wavelength will notconstructively interfere at that same angle, but will at some otherangle. Therefore, in spectrometers, for instance, the location thatlight appears relates to the specified output diffraction angles of thelight, and the respective wavelength of the light within the light beamthat entered the spectrometer.

FIG. 27 shows one embodiment of Echelle grating 2700 that is configuredto reflect different wavelengths of light (instead of diffracting light)through an output reflection angle. For instance, an input light beam2702 of a prescribed wavelength, as it contacts a grating surface 2704of a projected Echelle grating 2706, will reflect an output light beam2708 through an angle. The propagation constant of the region ofchangeable propagation constant 190 will generally have to be higherthan that for a diffraction Echelle grating. In addition, the angle atwhich the grating surface 2704 faces the oncoming input light beam 2702would probably be lower if the light is refracted, not reflected. Suchdesign modifications can be accomplished by reconfiguring the shape ofthe gate electrode in the optical waveguide device. Shaping the gateelectrodes is relatively inexpensive compared with producing a distinctdevice.

4D Optical Lenses

Waveguide lenses are important devices in integrated optical/electroniccircuits because they can perform various essential functions such asfocusing, expanding, imaging, and planar waveguide Fourier Transforms.

The FIG. 25 embodiment of Echelle grating 2500 can be used not only as adiffraction grating as described relative to FIG. 26, but the samestructure can also be biased to perform as a lens to focus light. To actas a lens, the polarity of the voltage of the Echelle grating 2500applied between the gate electrode and the combined first bodycontact/second body contact electrodes is opposite that shown for theFIG. 26 embodiment of diffraction grating.

FIGS. 28 and 29 show three input light beams that extend into the regionof altered propagation constant 190 in the waveguide are shown as 2806,2807, and 2809. The input light beams 2806, 2807, and 2809 are shown asextending substantially parallel to each other, and also substantiallyparallel to the side surfaces 2520, 2522 of the projected region ofchangeable propagation constant 190. The projected region of changeablepropagation constant 190 shown in FIGS. 28 and 29 generally mirrorsvertically through the height of the waveguide the shape and size of theFIG. 25 embodiment of Echelle shaped gate electrode 2502.

The light input from the input beams 2806, 2807, and 2809 extend throughthe region of changeable propagation constant 190 to form, respectively,the three sets of output beams 2810 a and 2810 b; 2812 a, 2812 b and2812 c; and 2814 a and 2814 b as shown in FIG. 28. Each focused outputbeam 2810, 2812, and 2814 is shown for a single wavelength of light, andthe output beam represents the direction of travel of a beam of light ofa specific wavelength with which that beam of light will constructivelyinterfere. In other directions, the light of the specific wavelengthdestructively interferes.

The lower input light beam 2806 that enters near the bottom of theprojected region of changeable propagation constant 190 travels for avery short distance d1 through the projected region of changeablepropagation constant 190 (as shown from the left to the right) and exitsas output beam 2810 a or 2810 b. As such, though the region ofchangeable propagation constant 190 has a different propagation constantthen the rest of the waveguide 106. The amount that the output beam 2810a is focused is very small when compared to the amount of focusing onthe other output beams 2812, 2814 that have traveled a greater distancethrough the region of changeable propagation constant 190.

The middle input light beam 2807 enters the projected region ofchangeable propagation constant 190 and travels through a considerabledistance d2 before exiting from the projected Echelle grating. If thereis no voltage applied to the gate electrode, then the output light willbe unaffected by the region of changeable propagation constant 190, andlight following input path 2807 will continue straight after exiting thewaveguide along 2812 a. If a medium voltage level is applied to the gateelectrode, then the propagation constant within the region of changeablepropagation constant 190 will not equal that within the surroundingwaveguide. The propagation constant in the region of changeablepropagation constant 190 will deflect light beam 2807 through an angleθ_(f1) along path 2812 b. If the voltage is increased, the amount ofdeflection for focusing is also increased to the angle shown at 2812 c.

Light corresponding to the input light beam 2809 will continue straightthrough the region of changeable propagation constant along line 2814 awhen no voltage is applied to the gate electrode. If a prescribed levelof voltage is applied to the gate electrode, the output light beam willbe focused through an output angle θ_(f2) to along output light beam2814 b. The output angle θ_(f2) of output focused beam 2814 b exceedsthe output angle θ_(f1) of focused beam 2812 b if the same voltageapplied to the gate electrode. The output angle varies linearly from oneside surface 2522 to the other side 2520, since the output angle is afunction of the distance the light is travelling through the projectedregion of changeable propagation constant 190.

FIGS. 28 and 29 demonstrate that a voltage can be applied to an Echelleshaped gate electrode 2602, and that it can be biased in a manner tocause the Echelle grating 2500 to act as a focusing device. The level ofthe voltage can be varied to adjust the focal length. For example,assume that a given projected region of changeable propagation constant190 results in the output focused beams 2810, 2812, and 2814 convergingat focal point f_(P1). Increasing the gate voltage will cause thepropagation constant in the projected region of changeable propagationconstant 190 to increase, resulting in a corresponding increase in theoutput focus angle for each of the output focused beams. As such, theoutput focus beams would converge at a different point, e.g., at focalpoint f_(P2), thereby, effectively decreasing the focal length of thelens. The FIGS. 28 and 29 embodiment of focusing mechanism can be usedin cameras, optical microscopes, copy machines, etc., or any device thatrequires an optical focus. There are no moving parts in this device,which simplifies the relatively complex auto focus devices that arepresently required for mechanical lenses. Such mechanical auto-focuslenses, for example, require precisely displacing adjacent lenses towithin a fraction of a wavelength.

FIG. 30 shows another embodiment of an optical waveguide device 100including a grating 3008 that is used as a lens to focus light passingthrough the waveguide. The embodiment of optical waveguide device 100,or more particularly the FIG. 2 embodiment of gate electrode of theoptical waveguide device, is modified by replacing the continuous gateelectrode (in FIG. 2) with a discontinuous electrode in the shape of agrating (shown in FIG. 30). The grating 3008 is formed with a pluralityof etchings 3010 that each substantially parallels the optical path 101of the optical waveguide device. In the FIG. 30 embodiment of grating3008, the thickness of the successive etchings 3010 to collectively formgate electrode 120 increases toward the center of the optical waveguidedevice, and decreases toward the edges 120 a, 120 b of the gateelectrode 120. Therefore, the region of changeable propagation constant190 in the waveguide is thicker at those regions near the center of thewaveguide. Conversely, the region of changeable propagation constant 190becomes progressively thinner at those regions of the waveguide nearedges 120 a, 120 b. The propagation constant is a factor of both thevolume and the shape of the material used to form the gate electrode.The propagation constant is thus higher for those regions of changeablepropagation constant closer to the center of the waveguide.

Light is assumed to be entering the waveguide 106 followingsubstantially parallel paths as shown by exemplary paths 3012 a and 3012b. Paths 3012 a and 3012 b represent two paths travelling at theoutermost positions of the waveguide. The locations between paths 3012 aand 3012 b are covered by a continuum of paths that follow similarroutes. When sufficient voltage is applied to the grating shapedelectrode, the light following paths 3012 a and 3012 b will be deflectedto follow output paths 3014 a and 3014 b, respectively. Output paths3014 a and 3014 b, as well as the paths of all the output paths thatfollow through the waveguide under the energized grating 3008 will bedeflected a slightly different amount, all toward a focus point 3016.The FIG. 30 embodiment of optical waveguide device therefore acts as alens. The grating 3008, though spaced a distance from the waveguide, canbe biased to direct the light in a manner similar to a lens.

The reason why the embodiment of grating shown in FIG. 30 acts as a lensis now described. Light travelling within the waveguide requires alonger time to travel across those regions of changeable propagationconstant at the center (i.e., taken vertically as shown in FIG. 30) thanthose regions adjacent the periphery of the lens (i.e., near edges 120a, 120 b). This longer time results because the propagation constant isgreater for those regions near the center. For light of a givenwavelength, light exiting the lens will meet at a particular focalpoint. The delay imparted on the light passing through the regions ofchangeable propagation constant nearer the center of the lens will bedifferent from that of the light passing near edges 120 a, 120 b. Thetotal time required for the light to travel to the focal point is madefrom the combination of the time to travel through the region ofchangeable propagation constant 190 added to the time to travel from theregion of changeable propagation constant 190 to the focal point. Thetime to travel through the region of changeable propagation constant 190is a function of the propagation constant of each region of changeablepropagation constant 190. The time to travel from the region ofchangeable propagation constant 190 to the focal point is a function ofthe distance from the region of changeable propagation constant 190 tothe focal point. As a result of the variation in propagation constantfrom the center of the waveguide toward the edges 120 a, 120 b, a givenwavelength of light arrives at a focal point simultaneously, and thelens thereby focuses light.

There has been increasing interest in waveguide lenses such as Fresnellenses and grating lenses. Such lenses offer limited diffractionperformance, and therefore they constitute a very important element inintegrated optic devices. Waveguide Fresnel lenses consist of periodicgrating structures that cause a spatial phase difference between theinput and the output wavefronts. The periodic grating structure gives awavefront conversion by spatially modulating the grating. Assuming thatthe phase distribution function of the input and output waves aredenoted by φ₁ and φ₂, respectively, the phase difference Δφ in theguided wave structure can be written as:Δφ=φ₀−φ₁  10

The desired wavefront conversion is achieved by a given phase modulationto the input wavefront equal to Δφ. The grating for such phasemodulation consists of grating lines described by:Δφ=2mπ  11

where m is an integer, and, for light having a specific wavelength, thelight from all of the grating lines will interfere constructively.

The phase difference Δφ for a planar waveguide converging wave followsthe expression:Δφ(x)=kn _(eff)(f−√{square root over (x ² +f ²))}  12

where f is the focal length, n_(eff) is the propagation constant of thewaveguide, and x is the direction of the spatial periodic gratingmodulation.

FIGS. 30 and 31 show two embodiments of optical waveguide devices thatperform waveguide Fresnel lens functions. The two-dimensional Fresnellenses follow the phase modulation like their three-dimensional lenscounterpart:φ_(F)(x)=Δφ(x)+2mπ  13

for x_(m)<|x|<x_(m+1), the phase modulation Δφ(x_(m))=2mπ, which isobtained by segmenting the modulation into Fresnel zones so thatφ_(F)(x) has amplitude 2π. Under the thin lens approximation, the phaseshift is given by KΔnL. Therefore, the phase of the wavefront for aspecific wavelength can be controlled by the variations of Δn and L. IfΔn is varied as a function of x, where the lens thickness, L, is heldconstant, as shown in FIG. 30, it is called the GRIN Fresnel lens and isdescribed by:Δn(x)=Δn _(max)(φ_(F)(x)/2π+1)  14

FIG. 32 shows one embodiment of optical waveguide device that operatesas a gradient-thickness Fresnel lens where Δn is held constant. Thethickness of the lens L has the following functional form:L(x)=L _(max)(φ_(F)(x)/2π+1)  15

To have 2π phase modulation, in either the FIG. 30 or FIG. 31 embodimentof lens, the modulation amplitude must be optimized. The binaryapproximation of the phase modulation results in the step-index Fresnelzone lens. The maximum efficiency of 90%, limited only by diffraction,can be obtained in certain lenses.

Another type of optical waveguide device has been designed by spatiallychanging the K-vector as a function of distance to the central axis,using a so-called chirped grating configuration. In chirped gratingconfigurations, the cross sectional areas of the region of changeablepropagation constant 190 are thicker near the center of the waveguidethan the periphery to provide a greater propagation constant as shown inthe embodiment of FIG. 30. Additionally, the output of each region ofchangeable propagation constant 190 is angled towards the focal point toenhance the deflection of the light toward the deflection point. Thearchitecture of the FIG. 32 embodiment of chirped grating waveguide lensresults in index modulation according to the equation:Δn(x)=Δn cos [Δφ(x)]=Δn cos {Kn _(e) [Kn _(e)(f−√x ² +f ²)]}  16

Where f=focal length, Δφ=phase difference; L is the lens thickness ofthe grating; x is the identifier of the grating line, and n is therefractive index. As required by any device based on grating deflection,the Q parameter needs to be greater than 10 to reach the region in orderto have high efficiency. The grating lines need to be slanted accordingto the expression:Ψ(x)=½ tan⁻¹(x/f)≅x/2f  17

so that the grating condition is satisfied over the entire aperture. Thecondition for maximum efficiency is:kL=πΔnL/λ=π2  18

In the embodiment of the optical waveguide device as configured in FIG.32, adjustments may be made to the path length of the light passingthrough the waveguide by using a gate electrode formed with compensatingprism shapes. Such compensating prism shapes are configured so that thevoltage taken across the gate electrode (from the side of the gateelectrode adjacent the first body contact electrode to the side of thegate electrode adjacent the second body contact electrode) varies. Sincethe voltage across the gate electrode varies, the regions of changeablepropagation constant will similarly vary across the width of thewaveguide. Such variation in the voltage will likely result in a greaterpropagation of the light passing through the waveguide at differentlocations across the width of the waveguide.

FIG. 33 shows a front view of another embodiment of optical waveguidedevice from that shown in FIG. 1. The optical waveguide device 100 shownin FIG. 33 is configured to operate as a lens 3300. The depth of theelectrical insulator layer 3302 varies from a maximum depth adjacent theperiphery of the waveguide to a minimum depth adjacent the center of thewaveguide. Due to this configuration, a greater resistance is providedby the electrical insulator 3302 to those portions that are adjacent theperiphery of the waveguide and those portions that are the center of thewaveguide. The FIG. 33 embodiment of optical lens can establish apropagation constant gradient across the width of the waveguide. Thevalue of the propagation constant will be greatest at the center, andlesser at the periphery of the waveguide. This embodiment of lens 3300may utilize a substantially rectangular gate electrode. It may also benecessary to provide one or more wedge shape spacers 3306 that are madefrom material having a lower electrical resistance than the electricalinsulator 3302 to provide a planer support surface to support the gateelectrode. Other embodiment in which the electrical resistance of theelectrical insulator is varied to change an electrical field at theinsulator/semiconductor interface resulting in a varied propagationconstant level are within the scope of the present invention.

4E. Optical Filters

The optical waveguide device 100 can also be modified to provide avariety of optical filter functions. Different embodiments of opticalfilters that are described herein include an arrayed waveguide (AWG)component that acts as a multiplexer/demultiplexer or linear phasefilter in which a light signal can be filtered into distinct bandwidthsof light. Two other embodiments of optical filters are afinite-impulse-response (FIR) filter and an infinite-impulse-response(IIR) filter. These embodiments of filters, as may be configured withthe optical waveguide device, are now described.

FIG. 34 shows one embodiment of an optical waveguide device beingconfigured as an AWG component 3400. The AWG component 3400 may beconfigured to act as a wavelength multiplexer, wavelength demultiplexer,a linear phase filter, or a router. The AWG component 3400 is formed ona substrate 3401 with a plurality of optical waveguide devices. The AWGcomponent 3400 also includes an input waveguide 3402 (that may be formedfrom one waveguide or an array of waveguides for more than one inputsignal), an input slab coupler 3404, a plurality of arrayed waveguidedevices 3410, an output slab coupler 3406, and an output waveguide array3408. The input waveguide 3402 and the output waveguide array 3408 eachcomprise one or more channel waveguides (as shown in the FIGS. 1 to 3,4, or 5 embodiments) that are each optically coupled to the input slabcoupler 3402. Slab couplers 3404 and 3406 allow the dispersion of light,and each slab coupler 3404 and 3406 may also be configured as in theFIGS. 1 to 3 or 5 embodiments. Each one of the array waveguides 3410 maybe configured as in the FIGS. 10 to 11 embodiment of channel waveguide.Controller 201 applies a variable DC voltage V_(g) to some or all of thewaveguide couplers 3402, 3404, 3406, 3408, and 3410 to adjust forvariations in temperature, device age and characteristics, or otherparameters as discussed above in connection with the FIGS. 7-8. In theembodiment shown, controller 201 does not have to apply an alternatingcurrent signal v_(g) to devices 3402, 3404, 3406, 3408, and 3410.

The input array 3402 and the input slab coupler 3404 interact to directlight flowing through one or more of the input waveguides of the channelwaveguides 3410 depending upon the wavelength of the light. Each arraywaveguide 3410 is a different length, and can be individually modulatedin a manner similar to described above. For example, the upper arraywaveguides, shown with the greater curvature, have a greater light pathdistance than the lower array waveguides 3410 with lesser curvature. Thedistance that light travels through each of the array waveguides 3410differs so that the distance of light exiting the different arraywaveguides, and the resultant phase of the light exiting from thedifferent array waveguides, differ.

Optical signals pass through the plurality of waveguides (of the channeland slab variety) that form the AWG component 3400. The AWG component3400 is often used as an optical wavelength divisiondemultiplexer/multiplexer. When the AWG component 3400 acts as anoptical wavelength division demultiplexer, one input multi-bandwidthsignal formed from a plurality of input component wavelength signals ofdifferent wavelengths is separated by the AWG component 3400 into itscomponent plurality of output single-bandwidth signals. The inputmulti-bandwidth signal is applied to the input waveguide 3402 and theplurality of output single-bandwidth signals exit from the outputwaveguide array 3408. The AWG component 3400 can also operate as amultiplexer by applying a plurality of input single-bandwidth signals tothe output waveguide array 3408 and a single output multi-bandwidthsignal exits from the input waveguide 3402.

When the AWG component 3400 is configured as a demultiplexer, the inputslab coupler 3404 divides optical power of the input multi-bandwidthsignal received over the input waveguide 3402 into a plurality of arraysignals. In one embodiment, each array signal is identical to each otherarray signal, and each array signal has similar signal characteristicsand shape, but lower power, as the input multi-bandwidth signal. Eacharray signal is applied to one of the plurality of arrayed waveguidedevices 3410. Each one of the plurality of arrayed waveguide devices3410 is coupled to the output terminal of the input slab coupler 3404.The AWG optical wavelength demultiplexer also includes the output slabcoupler 3406 coupled to the output terminal of the plurality of arrayedwaveguide devices 3410. Each arrayed waveguide device 3410 is adapted toguide optical signals received from the input slab coupler 3404 so eachone of the plurality of arrayed waveguide signals within each of therespective plurality of arrayed waveguide devices (that is about to exitto the output slab coupler) has a consistent phase shift relative to itsneighboring arrayed waveguides device 3410. The output slab coupler 3406separates the wavelengths of each one of the arrayed waveguide signalsoutput from the plurality of arrayed waveguide devices 3410 to obtain aflat spectral response.

Optical signals received in at least one input waveguide 3402 passthrough the input slab coupler 3404 and then enter the plurality ofarrayed waveguide devices 3410 having a plurality of waveguides withdifferent lengths. The optical signals emerging from the plurality ofarrayed waveguide devices 3410 have different phases, respectively. Theoptical signals of different phases are then incident to the output slabcoupler 3406 in which a reinforcement and interference occurs for theoptical signals. As a result, the optical signals are focused at one ofthe output waveguide array 3408. The resultant image is then outputtedfrom the associated output waveguide array 3408.

AWG optical wavelength demultiplexers are implemented by an arrayedwaveguide grating configured to vary its wavefront direction dependingon a variation in the wavelength of light. In such AWG opticalwavelength demultiplexers, a linear dispersion indicative of a variationin the shift of the main peak of an interference pattern on a focalplane (or image plane) depending on a variation in wavelength can beexpressed as follows: $\begin{matrix}{\frac{\mathbb{d}_{x}}{\mathbb{d}\lambda} = \frac{fm}{n_{s}d}} & 19\end{matrix}$

where “f” represents the focal distance of a slab waveguide, “m”represents the order of diffraction, “d” represents the pitch of one ofthe plurality of arrayed waveguide devices 3410, and “n_(s)” is theeffective refractive index of the slab waveguide. In accordance withequation 19, the wavelength distribution of an optical signal incidentto the AWG optical wavelength demultiplexer is spatially focused on theimage plane of the output slab coupler 3406. Accordingly, where aplurality of output waveguides in array 3408 are coupled to the imageplane while being spaced apart from one another by a predetermineddistance, it is possible to implement an AWG optical wavelengthdemultiplexer having a wavelength spacing determined by the location ofthe output waveguide array 3408.

Optical signals respectively outputted from the arrayed waveguides ofthe AWG component 3400 while having different phases are subjected to aFraunhofer diffraction while passing through the output slab coupler3406. Accordingly, an interference pattern is formed on the image planecorresponding to the spectrum produced by the plurality of outputsingle-bandwidth signals. The Fraunhofer diffraction relates the inputoptical signals to the diffraction pattern as a Fourier transform.Accordingly, if one of the input multi-bandwidth signals is known, it isthen possible to calculate the amplitude and phase of the remaininginput multi-bandwidth signals using Fourier transforms.

It is possible to provide phase and/or spatial filters that filter theoutput single-bandwidth signals that exit from the output waveguidearray 3408. U.S. Pat. No. 6,122,419 issued on Sep. 19, 2000 to Kurokawaet al. (incorporated herein by reference) describes different versionsof such filtering techniques.

FIG. 35 shows one embodiment of a finite-impulse-response (FIR) filter3500. The FIR filter 3500 is characterized by an output in a linearcombination of present and past values of inputs. In FIG. 35, x(n) showsthe present value of the input, and x(n-1), x(n-2), etc. represent therespective previous values of the input; y(x) represents the presentvalue of the output; and h(1), h(2) represent the filter coefficients ofx(n), y(n-1), etc. The D corresponds to the delay. The FIR filter 3500satisfies equation 20: $\begin{matrix}{y = {\sum\limits_{k = 0}^{M}\quad{{h(k)}{x\left( {n - k} \right)}}}} & 20\end{matrix}$

An AWG, for example, is one embodiment of FIR filter in which thepresent output is a function entirely of past input. One combination ofoptical waveguide devices, a top view of which is shown in FIG. 36, is aFIR filter 3600 known as a coupled waveguide 3600. The coupled waveguide3600, in its most basic form, includes a first waveguide 3602, a secondwaveguide 3604, a coupling 3606, and a light pass grating 3608. Thefirst waveguide 3602 includes a first input 3610 and a first output3612. The time necessary for light to travel through the first waveguide3602 and/or the second waveguide 3604 corresponds to the delay D shownin the FIG. 35 model of FIR circuit. The second waveguide 3604 includesa second input 3614 and a second output 3616.

The coupling 3606 allows a portion of the signal strength of the lightflowing through the first waveguide 3602 to pass into the secondwaveguide 3604, and vice versa. The amount of light flowing between thefirst waveguide 3602 and the second waveguide 3604 via the coupling 3606corresponds to the filter coefficients h(k) in equation 20. Oneembodiment of light pass grating 3608 is configured as a grating asshown in FIGS. 20 to 22. Controller 201 varies the gate voltage of thelight pass grating to control the amount of light that passes betweenthe first waveguide 3602 and the second waveguide 3604, and compensatesfor variations in device temperature. An additional coupling 3606 andlight pass grating 3608 can be located between each additional pair ofwaveguides that have a coefficient as per equation 20.

FIG. 37 shows one embodiment of a timing model of aninfinite-impulse-response (IIR) filter 3700. The FIG. 37 model of IIRfilter is characterized by an output that is a linear combination of thepresent value of the input and past values of the output. The IIR filtersatisfies equation 21: $\begin{matrix}{{y(n)} = {{x(n)} + {\sum\limits_{k = 1}^{M}\quad{\alpha_{k}{y\left( {n - k} \right)}}}}} & 21\end{matrix}$

Where x(n) is a present value of the filter input; y(n) is the presentvalue of the filter output; y(n-1), etc. are past values of the filteroutput; and α₁, . . . , α_(M) are the filter coefficients.

One embodiment of an IIR filter 3800 is shown in FIG. 38. The IIR filter3800 includes an input waveguide 3801, a combiner 3802, a waveguide3803, an optical waveguide device 3804, a waveguide 3805, a beamsplitter 3806, an output waveguide 3807, and a delay/coefficient portion3808. The delay/coefficient portion 3808 includes a waveguide 3809, avariable optical attenuator (VOA) 3810, and waveguide 3812. Thedelay/coefficient portion 3808 is configured to provide a prescribedtime delay to the optical signals passing from the beam splitter 3806 tothe combiner 3802. In the FIG. 38 embodiment of an IIR filter 3800, thetime necessary for light to travel around a loop defined by elements3802, 3803, 3804, 3805, 3806, 3809, 3810, and 3812 once equals the delayD shown in the FIG. 37 model of IIR circuit. The variable opticalattenuator 3810 is configured to provide a prescribed amount of signalattenuation to correspond to the desired coefficient, α₁ to α_(M). Anexemplary VOA is described in connection with FIG. 41 below.

Input waveguide 3801 may be configured, for example, as the channelwaveguide shown in FIGS. 1 to 3, 4, or 5. Combiner 3802 may beconfigured, for example, as a grating shown in FIGS. 20 to 22 integratedin a slab waveguide shown in the FIGS. 1 to 3, 4, or 5. The waveguide3803 may be configured, for example, as the channel waveguide shown inFIGS. 1 to 3, 4, or 5. The optical waveguide device 3804 may beconfigured, for example, as the channel waveguide shown in FIGS. 1 to 3,4, or 5. The waveguide 3805 may be configured, for example, as thechannel waveguide shown in FIGS. 1 to 3, 4, or 5. The beam splitter 3806may be configured, for example, as the beamsplitter shown below in FIG.46. The waveguide 3809 may be configured, for example, as the channelwaveguide shown in FIGS. 1 to 3, 4, or 5. The VOA 3810 may be configuredas shown below relative to FIG. 41. The waveguide 3812 may beconfigured, for example, as the channel waveguide shown in FIGS. 1 to 3,4, or 5.

Controller 201 applies a variable DC voltage V_(g) to the respectivegate electrodes of the input waveguide 3801, the combiner 3802, thewaveguide 3803, the optical waveguide device 3804, the waveguide 3805,the beam splitter 3806, the waveguide 3809, the VOA 3810, and thewaveguide 3812 to adjust for variations in temperature, device age,device characteristics, etc. as discussed below in connection with FIGS.7-8. In addition, controller 201 also varies the gate voltage applied toother components of the IIR to vary their operation, as discussed below.

During operation, an optical signal is input into the waveguide 3801.Virtually the entire signal strength of the input optical signal flowsthrough the combiner 3802. The combiner 3802 is angled to a sufficientdegree, and voltage is applied to a sufficient amount so the propagationconstant of the waveguide is sufficiently low to allow the light fromthe waveguide 3801 to pass directly through the combiner 3802 to thewaveguide 3803. The majority of the light that passes into waveguide3803 continues to the optical waveguide device 3804. The opticalwaveguide device 3804 can perform a variety of functions upon the light,including attenuation and/or modulation. For example, if it is desiredto input digital signals, the optical waveguide device 3804 can bepulsed on and off as desired when light is not transmitted to the outputwaveguide 3807 by varying the gate voltage of waveguide device 3804. Ifthe optical waveguide device 3804 is turned off and is fullyattenuating, then a digital null signal will be transmitted to theoutput waveguide 3807.

The output signal from the output waveguide device 3804 continuesthrough waveguide 3805 into beam splitter 3806. Beam splitter 3806diverts a prescribed amount of the light into waveguide 3809, and alsoallows prescribed amount of the light to continue onto the outputwaveguide 3807. The voltage applied to the gate of the beam splitter3806 can be changed by controller 201 to control the strength of lightthat is diverted to waveguide 3809 compared to that that is allowed topass to output waveguide 3807.

The light that is diverted through waveguide 3809 continues through thevariable optical attenuator 3810. The voltage applied to the variableoptical attenuator (VOA) 3810 can be adjusted depending upon the desiredcoefficient. For example, full voltage applied to the gate electrode ofthe VOA 3810 would fully attenuate the light passing through thewaveguide. By comparison, reducing the voltage applied to the gateelectrode would allow light to pass through the VOA to the waveguide3812. Increasing the amount of light passing through the VOA acts toincrease the coefficient for the IIR filter corresponding to thedelay/coefficient portion 3808. The light that passes through to thewaveguide 3812 continues on to the combiner 3802, while it is almostfully deflected into waveguide 3803 to join the light that is presentlyinput from the input waveguide 3801 through the combiner 3802 to thewaveguide 3803. However, the light being injected from waveguide 3812into the combiner 3803 is delayed from the light entering from the inputwaveguide 3801. A series of these IIR filters 3800 can be arrangedserially along a waveguide path.

FIGS. 39 and 40 show two embodiments of a dynamic gain equalizer thatacts as a gain flattening filter. The structure and filtering operationof the dynamic gain equalizer is described below.

4F. Variable Optical Attenuators

A variable optical attenuator (VOA) is used to controllably attenuateone or more bandwidths of light. The VOA is an embodiment of opticalamplitude modulators, since optical attenuation may be considered a formof amplitude modulation. FIG. 41 shows one embodiment of a VOA 4100 thatis modified from the FIGS. 1 to 3 or 5 embodiment of optical waveguidemodulators. The VOA 4100 includes multiple sets of patterned gratings4102 a, 4102 b, and 4102 c, multiple gate electrodes 4104 a, 4104 b, and4104 c, multiple variable voltage sources 4106 a, 4106 b, and 4106 c,and a monitor 4108. Each individual plane in the patterned gratings 4102a, 4102 b, and 4102 c are continuous even through they are depictedusing dotted lines (since they are located behind, or on the backsideof, the respective gate electrodes 4104 a, 4104 b, and 4104 c).

Each of the multiple sets of patterned gratings 4102 a, 4102 b, and 4102c correspond, for example, to the embodiments of grating shown in FIGS.20-22, and may be formed in the electrical insulator layer or eachrespective gate electrode. The respective gate electrode 4104 a, 4104 b,or 4104 c, or some insulative pattern is provided as shown in the FIGS.20 to 22 embodiments of gratings. In any one of the individual patternedgratings 4102 a, 4102 b, and 4102 c, the spacing between adjacentindividual gratings is equal. However, the spacing between individualadjacent gratings the FIG. 41 embodiment of patterned gratings 4102 a,4102 b, and 4102 c decreases from the light input side to light outputside (left to right). Since the grating size for subsequent patternedgratings 4102 a, 4102 b, and 4102 c decreases, the wavelength of lightrefracted by each also decreases from input to output.

Each patterned gratings 4102 a-4102 c has a variable voltage sourceapplied between its respective gate electrode 4104 a, 4104 b, and 4104 cand its common voltage first body contact electrode/second body contactelectrode. As more voltage is applied between each of the variablevoltage sources 4106 a, 4106 b, and 4106 c and the gratings 4102 a to4102 c, the propagation constant of that patterned grating increases.Consequently, more light of the respective wavelengths λ₁, λ₂, or λ₃associated with the spacing of that patterned gratings 4102 a to 4102 cwould be refracted, and interfere constructively. The monitor 4108 canmonitor such light that interferes constructively.

Depending upon the intensity of the refracted light at each wavelength,equation 22 applies.P _(R)(λ₁)+P _(T)(λ₁)=P ₀(λ₁)  22

where P_(R)(λ₁) equals the refracted light, P_(T)(λ₁) equals thetransmitted light, and P₀(λ₁) equals the output light. In a typicalembodiment, a variable optical attenuator 4100 may be arranged with,e.g., 50 combined patterned gratings and gate electrodes (though onlythree are shown in FIG. 41). As such, light having 50 individualbandwidths could be attenuated from a single light beam using thevariable optical attenuator 4100.

4G. Programmable Delay Generators and Optical Resonators

Programmable delay generators are optical circuits that add aprescribed, and typically controllable, amount of delay to an opticalsignal. Programmable delay generators are used in such devices asinterferometers, polarization control, and optical interferencetopography that is a technology used to examine eyes. In all of thesetechnologies, at least one optical signal is delayed. FIG. 42 shows atop view of one embodiment of a programmable delay generator 4200. FIG.43 shows a side cross sectional view of the FIG. 42 embodiment ofprogrammable delay generator 4200. In addition to the standardcomponents of the optical waveguide device shown in the embodiments ofFIGS. 1-3, 4, or 5, the programmable delay generator 4200 includes aplurality of grating devices 4202 a to 4202 e and a plurality of axiallyarranged gate electrodes 120. The embodiment of gratings devices 4202shown in FIGS. 42 and 43 are formed in the lower surface of the gateelectrode, however, the grating devices may alternatively be formed asshown in the embodiments in FIGS. 20 to 22 as grooves in the lowersurface of the electrical insulator, as insulator elements havingdifferent resistance inserted in the insulator, as grooves formed in thelower surface of the gate electrode, or as some equivalent gratingstructure such as using surface acoustic waves that, as with the othergratings, project a series of parallel planes 4204, representing regionsof changeable propagation constant, into the waveguide. The spacingbetween the individual grooves in the grating equals some multiple ofthe wavelength of light that to be reflected.

Each axially arranged gate electrode 120 is axially spaced a shortdistance from the adjacent gate electrodes, and the spacing depends uponthe amount by which the time delay of light being reflected within theprogrammable delay generator 4200 can be adjusted. During operation, agate voltage is applied to one of the axially arranged gate electrodes120 sufficient to increase the strength of the corresponding region ofchangeable propagation constant sufficiently to reflect the lighttravelling within the optical waveguide device.

As shown in FIG. 43, the gate electrode from grating device 4202 c isenergized, so incident light path 4302 will reflect off the region ofchangeable propagation constant 190 associated with that gate electrodeand return along return light path 4304. The delay applied to lighttravelling within the channel waveguide is therefore a function of thelength of the channel waveguide between where light is coupled intoand/or removed from the channel waveguide and where the actuated gateelectrode projects its series of planes or regions of changeablepropagation constant. The light has to travel the length of the incidentpath and the return path, so the delay provided by the programmabledelay generator generally equals twice the incident path length dividedby the speed of light. By electronically controlling which of thegrating devices 4202 a to 4202 e are actuated at any given time, thedelay introduced by the delay generator 4200 can be dynamically varied.

In one embodiment of operation for the programmable delay generator4200, only one axially arranged gate electrode 120 is energized withsufficient strength to reflect all the light since that electrode willreflect all of the light travelling within the waveguide. Thisembodiment provides a so-called hard reflection since one plane orregions of changeable propagation constant reflects all of the incidentlight to form the return light.

In another embodiment of operation for the programmable delay generator4200, a plurality of adjacent, or axially spaced as desired, gateelectrodes 120 are energized using some lesser gate voltage level thanapplied in the prior embodiment to reflect all of the light. The planesor regions of changeable propagation constant associated with eachactuated axially arranged gate electrode 120 each reflect somepercentage of the incident light to the return light path. The latterembodiment uses “soft” reflection since multiple planes or regions ofchangeable propagation constant reflect the incident light to form thereturn light.

Optical resonators are used to contain light within a chamber (e.g. thechannel waveguide) by having the light reflect between optical mirrorslocated at the end of that waveguide. The FIG. 44 embodiment ofresonator 4400 is configured as a channel waveguide so the light isconstrained within two orthogonal axes due to the total internalreflectance (TIR) of the channel waveguide. Light is also constrainedalong the third axis due to the positioning of TIR mirrors at eachlongitudinal end of the waveguide. The optical resonator 4400 forms atype of Fabry-Perot resonator. Resonators, also known as opticalcavities, can be integrated in such structures as lasers.

The resonator 4400 includes a optical waveguide of the channel type, oneor more input mirror gate electrodes 4402, one or more output mirrorgate electrodes 4404, and controllable voltage sources 4406 and 4408that apply voltages to the input mirror gate electrodes 4402 and theoutput mirror gate electrodes 4404, respectively. FIG. 45 shows a topview of the channel waveguide of the resonator 4400 of FIG. 44. Thechannel waveguide includes, when the voltage sources 4406 and/or 4408are actuated, an alternating series of high propagation constant bands4502 and low propagation constant bands 4504.

The high propagation constant bands 4502 correspond to the location ofthe input mirror gate electrodes 4402 or the output mirror gateelectrodes 4404. The low propagation constant bands 4504 correspond tothe bands between the input mirror gate electrodes 4402 or the outputmirror gate electrodes 4404. The high propagation constant bands 4502and the low propagation constant bands 4504 extend vertically throughthe waveguide. The input mirror gate electrodes 4402 and the outputmirror gate electrodes 4404 can be shaped to provide, e.g., a concavemirror surface if desired. Additionally, deactuation of the input mirrorgate electrodes 4402 or the output mirror gate electrodes 4404 removesany effect of the high propagation constant bands 4502 and lowpropagation constant bands 4504 from the waveguide of the resonator4400. Such effects are removed since the propagation constant approachesa uniform level corresponding to 0 volts applied to the gate electrodes4402, 4404.

As light travels axially within the waveguide of the resonator 4400,some percentage of the light will reflect off any one of one or morejunctions 4510 between each high propagation constant band 4502 and theadjacent low propagation constant band 4504, due to the reducedpropagation constant. Reflection off the junctions 4510 between highindex areas and low index areas forms the basis for much of thin filmoptical technology. The junction 4510 between each high propagationconstant band 4502 and the adjacent low propagation constant band 4504can be considered analogous to gratings. The greater the number of, andthe greater the strength of, such junctions 4510, the more light thatwill be reflected from the respective input mirror gate electrodes 4402or the output mirror gate electrodes 4404. Additionally, the greater thevoltage applied from the controllable voltage sources 4406 and 4408 tothe respective input mirror gate electrodes 4402 or the output mirrorgate electrodes 4404, the greater the difference in propagation constantbetween the high propagation constant band 4502 and the adjacent lowpropagation constant band 4504 for the respective input mirror gateelectrodes 4402 or the output mirror gate electrodes 4404.

FIG. 46 shows a top view of one embodiment of beamsplitter 4600 that isformed by modifying the optical waveguide device 100 shown in FIG. 46.The beamsplitter includes an input mirror 4602 having a first face 4604and a second face 4606. The mirror 4602 may be established in thewaveguide in a similar manner to a single raised land to provide avaried electrical field at the insulator/semiconductor interface in oneof the embodiments of gratings shown in FIGS. 20 to 22. The voltagelevel applied to the gate electrode 120 is sufficient to establish arelative propagation constant level in the region of changeablepropagation constant to reflect desired percentage of light followingincident path 101 to follow path 4610. The region of changeablepropagation constant takes the form of the mirror 4602. Light followingincident path 101 that is not reflected along path 4610 continuesthrough the mirror 4602 to follow the path 4612. Such mirrors 4602 alsoreflect a certain percentage of return light from path 4612 to followeither paths 4614 or 101. Return light on path 4610 that encountersmirror 4602 will either follow path 101 or 4614. Return light on path4614 that encounters mirror 4602 will either follow path 4612 or path4610. The strength of the voltage applied to the gate electrode 120 andthe resulting propagation constant level of the region of changeablepropagation constant in the waveguide, in addition to the shape and sizeof the mirror 4602 determine the percentage of light that is reflectedby the mirror along the different paths 101, 4610, 4612, and 4614.

4H. Optical Application Specific Integrated Circuits (OASICS)

Slight modifications to the optical functions and devices such asdescribed in FIGS. 16 to 25, taken in combination with free-carrierbased active optics, can lead to profound changes in optical designtechniques. Such modifications may only involve minor changes to thestructure of the gate electrode.

The optical waveguide device may be configured as a variable opticalattenuator that changes voltage between the gate electrode, the firstbody contact electrode, and the second body contact electrode, such thata variable voltage is produced across the width of the waveguide. Thisconfiguration results in a variable attenuation of the light flowingthrough the waveguide across the width of the waveguide.

If a magnetic field is applied to the 2DEG, then the free-carriersexhibit birefringence. The degree of birefringence depends on themagnitude of the magnetic field, the free-carrier or 2DEG density, andthe direction of propagation of the optical field relative to themagnetic field. The magnetic field may be generated by traditionalmeans, i.e. from passing of current or from a permanent magnet. Themagnetic field induced birefringence can be harnessed to make variousoptical components including polarization retarders, mode couplers, andisolators.

V. Optical Circuits Including Optical Waveguide Devices

5A. Optical Circuits

The optical functions of the optical waveguide devices described abovecan be incorporated onto one (or more) chip(s) in much the same way asone currently designs application specific integrated circuits (ASICS)and other specialized electronics, e.g., using standard libraries andspice files from a foundry. The optical functions of the opticalwaveguide devices described herein can be synthesized and designed inmuch the same way as electronic functions are, using ASICS. One may usean arithmetic logic unit (ALU) in a similar manner that ASICS arefabricated. This level of abstraction allowed in the design of opticalcircuits by the use of optical waveguide devices improves the capabilityof circuit designers to create and fabricate such large scale andinnovative designs as have been responsible for many of thesemiconductor improvements in the past.

As discussed above, different devices can be constructed by modifyingthe basic structure described in FIG. 1 by, e.g. changing the shape,configuration, or thickness of the gate electrode. These modifieddevices can provide the building blocks for more complex circuits, in asimilar manner that semiconductor devices form the basic building blocksfor more complex integrated circuit structures.

The disclosure now describes a variety of integrated optical/electroniccircuits that can be constructed using a plurality of optical waveguidedevices of the type described above. The integrated optical/electroniccircuits described are illustrative in nature, and not intended to belimiting in scope. Following this description, it becomes evident thatthe majority of functions that are presently performed by using currentintegrated circuits can also be formed using integratedoptical/electronic circuits. The advantages are potential improvement inoperating circuit capability, cost, and power consumption. It is to beunderstood that certain ones of the functions shown as being performedby an active optical waveguide device in the following integratedoptical/electronic circuits may also be performed using a passivedevice. For example, devices 4708 and 4712 in the embodiment shown inFIG. 47 may be performed by either active devices or passive devices.The embodiment of beamsplitter 4600 shown in FIG. 46 can either be anactive or passive device. The selection of whether to use an active orpassive device depends, e.g., on the operation of the integratedoptical/electronic circuit with respect to each particular opticalwaveguide device, and the availability of each optical waveguide devicein active or passive forms.

It is emphasized that the multiple optical waveguide devices of thetypes described above relative to FIGS. 1-3, 4, or 5 may be combined indifferent ways to form the following described integratedoptical/electronic circuits shown, for example, in the embodiments ofFIGS. 18, 19, 34, 36, 38-45, and 47-49. For example, the differentintegrated optical/electronic circuit embodiments may be formed using aplurality of optical waveguide devices formed on a single substrate.More particularly, the different embodiments of integratedoptical/electronic circuits may comprise multiple optical waveguidedevices attached to different portions of a single waveguide.Alternatively, the different embodiments of integratedoptical/electronic circuits including multiple optical waveguide devicesmay be formed on a plurality of discrete optical waveguide devices.

5B. Dynamic Gain Equalizer

FIG. 39 shows one embodiment of a dynamic gain equalizer 3900 comprisinga plurality of optical waveguide devices. The dynamic gain equalizer3900 comprises a wavelength separator 3902 (that may be, e.g. an arrayedwaveguide or an Echelle grating), a beam splitter 3904, a monitor 3906,the controller 201, a variable optical attenuator bank 3910, a wavelength combiner 3912, and an amplifier 3914. Dynamic gain equalizers arecommonly used to equalize the strength of each one of a plurality ofsignals that is being transmitted over relatively long distances. Forexample, dynamic gain equalizers are commonly used in long distanceoptical telephone cables and a considerable portion of the signalstrength is attenuated due to the long transmission distances between,e.g., states or countries.

The wavelength separator 3902 acts to filter or modulate the wavelengthof an incoming signal over waveguide 3916 into a plurality of lightsignals. Each of these light signals has a different frequency. Each ofa plurality of waveguides 3918 a to 3918 d contain a light signal ofdifferent wavelength λ₁ to λ_(n), the wavelength of each signalcorresponds to a prescribed limited bandwidth. For example, waveguide3918 a carries light having a color corresponding to wavelength λ₁,while waveguide 3918 b carries a light having a color corresponding towavelength λ₂, etc.

Each of the waveguides 3918 a to 3918 d is input into the beam splitter3904. The beam splitter outputs a portion of its light into a variableoptical attenuator 3910, and also deflects a portion of its light to themonitor 3906. The monitor 3906 senses the proportional signal strengththat is being carried over waveguide 3918 a to 3918 d. Both the monitor3906 and the beam splitter 3904 may be constructed using the techniquesfor the optical waveguide devices described above. The controller 201receives a signal from the monitor that indicates the signal strength ofeach monitored wavelength of light being carried over waveguides 3918 ato 3918 d.

The controller monitors the ratios of the signal strengths of thedifferent wavelength bands of light carried by waveguides 3918 a to 3918d, and causes a corresponding change in the operation of the variableoptical attenuator bank 3910. The variable optical attenuator bank 3910includes a plurality of variable optical attenuators 3930 a, 3930 b,3930 c and 3930 d that are arranged in series. Each VOA selectivelyattenuates light that originally passed through one of the respectivewaveguides 3918 a to 3918 d. The number of variable optical attenuators3930 a to 3930 d in the variable optical attenuator bank 3910,corresponds to the number of light bands that are being monitored overthe waveguides 3918 a to 3918 d. If the signal strength of one certainlight band is stronger than another light band, e.g., assume that thelight signal travelling through waveguide 3918 a is stronger than thelight signal travelling through 3918 b, then the stronger opticalsignals will be attenuated by the desired attenuation level by thecorresponding attenuator. Such attenuation makes the strength of eachoptical signal substantially uniform.

As such, all of the signal strengths on the downstream side of thevariable optical attenuators 3930 a, 3930 b, 3930 c and 3930 d should besubstantially equal, and are fed into a wavelength signal combiner 3912,where all the signals are recombined into a single signal. The opticalsignal downstream of the wavelength combiner 3912, therefore, is gainequalized (and may be considered as gain flattened). The signaldownstream of the wavelength combiner 3912 may still be relatively weakdue to a faint original signal or the relative attenuation of eachwavelength by the variable optical attenuator. Therefore, the signal isinput into the amplifier 3914. The amplifier, that in one embodiment isan Erbium Doped Fiber Amplifier (EDFA), amplifies the strength of thesignal uniformly across the different bandwidths (at least from λ₁ toλ_(n)) to a level where it can be transmitted to the next dynamic gainequalizer some distance down output waveguide 3932. Using thisembodiment, optical signals can be modulated without being convertedinto, and from, corresponding electronic signals. The variable opticalattenuators 3930 a to 3930 d and the wave length combiner 3912 can beproduced and operated using the techniques described above relating tothe optical waveguide devices.

FIG. 40 shows another embodiment of a dynamic gain equalizer 4000. Thebeam splitter 4004 and the monitor 4006 are components in the FIG. 40embodiment of dynamic gain equalizer 4000 that are located differentlythan in the FIG. 39 embodiment of dynamic gain equalizer 3900. The beamsplitter 4004 is located between the variable optical attenuator (VOA)bank 3910 and the wavelength combiner 3912. The wavelength combiner 3912may be fashioned as an arrayed waveguide (AWG) as shown in theembodiment of FIG. 34 (in a wavelength multiplexing orientation). Thebeam splitter 4004 is preferably configured to reflect a relativelysmall amount of light from each of the respective VOAs 3930 a, 3930 b,3930 c, and 3930 d. The beam splitter 4004 is configured to reflect aprescribed percentage of the light it receives from each of the VOAs3930 a to 3930 d to be transmitted to the monitor 4006. The monitor 4006converts the received light signals which relate to the strength of theindividual light outputs from the VOAs 3930 a to 3930 d into a signalwhich is input to the controller 201. The controller 201, whichpreferably is configured as a digital computer, an application specificintegrated-circuit, or perhaps even an on chip controller, determinesthe strengths of the output signals from each of the respective VOAs3930 a to 3930 d and balances the signal strengths by selectiveattenuation. For example, assume that the output signal of VOA2 3930 bis stronger than that of VOA3 3930 c, as well as the rest of the VOAs. Asignal attenuator would be actuated to attenuate the VOA2 3930 b signalappropriately. As such, the controller 201 selectively controls theattenuation levels of the individual VOAs 3930 a to 3930 d.

Each output light beam from VOAs 3930 a to 3930 d that continuesstraight through the beam splitter 4004 is received by the wavelengthcombiner 3912, and is combined into a light signal that contains all thedifferent wavelength signals from the combined VOAs 3930 a to 3930 d.The output of the wavelength 3912 is input into the amplifier, and theamplifier amplifies the signal uniformly to a level wherein it can betransmitted along a transmission waveguide to, for example, the nextdynamic gain equalizer 4000.

5C. Self Aligning Modulator

The FIG. 47 embodiment of self-aligning modulator 4700 is another systemthat performs an optical function that may include a plurality ofoptical waveguide devices. The self-aligning modulator 4700 includes aninput light coupler 4702, a first deflector 4704, a second deflector4706, an input two dimensional lens 4708 (shown as a grating type lens),a modulator 4710, an output two dimensional lens 4712 (shown as agrating type lens), an output light coupler 4716, and the controller201.

The input light coupler 4702 acts to receive input light that is to bemodulated by the self-aligning modulator 4700, and may be provided byany type of optical coupler such as an optical prism. The firstdeflector 4704 and the second deflector 4706 are directed to operate inopposed lateral directions relative to the flow of light through theself-aligning modulator 4700. The input two dimensional lens 4708 actsto focus light that it receives from the deflectors 4704 and 4706 so thelight can be directed at the modulator 4710. The modulator 4710modulates light in the same manner as described above. The modulator maybe formed as one of the optical waveguide devices shown in FIGS. 1-3, 4,and 5. The deflected light applied to the modulator 4710 is both alignedwith the modulator and focused. The output two-dimensional lens 4712receives light output from the modulator 4710, and focuses the lightinto a substantially parallel path so that non-dispersed light can bedirected to the output light coupler 4716. The output light coupler 4716receives light from the output two-dimensional lens 4712, and transfersthe light to the outside of the self-aligning modulator 4700. Thecontroller 201 may be, e.g., a microprocessor formed on a substrate4720. The controller 201 controls the operation of all the activeoptical waveguide devices 4704, 4706, 4708, 4710, and 4712 included onthe self-aligning modulator 4700.

While the modulator 4710 and the two-dimensional lenses 4708, 4712 areshown as active optical waveguide devices, it is envisioned that one ormore passive devices may be substituted while remaining within the scopeof the present invention. The two-dimensional lenses 4708, 4712 areoptional, and the self-aligning modulator will operate with one or noneof these lenses. During operation, the first deflector 4704 and thesecond deflector 4706 are adjusted to get the maximum output lightstrength through the output light coupler 4716.

The self-aligning modulator 4700 ensures that a maximum, or specifiedlevel, amount of light applied to the input light coupler 4702 ismodulated by the modulator 4710 and released to the output light coupler4716. The performance of the self-aligning modulator system 4700 canalso be checked simultaneously. For instance, if light exiting from theoutput light coupler is reduced, the deflectors, the lenses, and themonitor may each be individually varied to determine whether it causesany improvement in operation. Other suitable control techniques andalgorithms may be used to derive an optimal operation. FIGS. 47, 48, and49 further demonstrate how a variety of optical waveguide devices may belocated on a single substrate or chip.

One or more optical waveguide devices may be configured as amulti-function optical bench that facilitates alignment of a laser tothe fiber. In the optical bench configuration, that is structuredsimilarly to the FIG. 47 embodiment of the self-aligning modulator 4700,a plurality of the FIGS. 1 to 3, 4, or 5 embodiments of opticalwaveguide devices are integrated on the substrate. For example, awaveguide can be formed in the substrate so that only the gateelectrode, the first body contact electrode, the second body contactelectrode, and the electrical insulator layer have to be affixed to thesubstrate to form the FET portion. The corresponding FET portions areattached to the substrate (the substrate includes the waveguide). Assuch, it is very easy to produce a wide variety of optical waveguidedevices.

5D. Optical Systems Using Delay Components

FIGS. 48 and 49 show several embodiments of systems that my beconstructed using one or more of the embodiments of programmable delaygenerator 4200 shown in FIGS. 42 and 43. FIGS. 48 shows one embodimentof a polarization controller. FIG. 49 shows one embodiment ofinterferometer.

Polarization control is a method used to limit interference between aplurality of different polarizations that occur, for example, when lightis transmitted in a fiber for a large distance such as 3,000 kilometersor more. Light that is to be transmitted over the fiber is often splitinto two polarizations, referred to as P polarization and Spolarization. The polarization is received at the other end of the fiberin some arbitrary polarization state since the fiber may encounterdifferent propagation constants for the P polarization signal and the Spolarization signal. Therefore, the P polarization signal and the Spolarization signal may be modulated within the fiber differently, andmay travel at different rates, and may be attenuated differently. Forexample, the duration between a first polarization and a secondpolarization may extend from a duration indicated as d to a longerduration shown as d′ as the signal is transmitted over a longtransmission fiber. When multiple data bits are transmitted, the Ppolarization signal and the S polarization signal for adjacent bits mayoverlap due to the different velocities of the polarizations. Forexample, one polarization of the previous bit is overlapping with theother polarization of the next bit. If a network exceeds a hundredpicoseconds at 10 gigahertz, there is a large potential for suchoverlap. An example of such a network is Network Simplement, a nextgeneration network presently under development in France.

The embodiment of polarization controller 4800 shown in FIG. 48comprises a transmission fiber 4802, an output 4804, an adjustablepolarizer 4806, a beamsplitter 4808, a first path 4810, a second path4812, and a combiner 4813 that combines the first path and the secondpath. The first path 4810 includes a programmable delay generator 4814.The second path 4812 comprises a programmable delay generator 4816. Thetransmission fiber 4802 may be fashioned as a channel waveguide oroptical fiber. The adjustable polarizer 4806 may be fashioned as a slabwaveguide. The beamsplitter 4808 may be fashioned as the beamsplitter4600 shown and described relative to FIG. 46. The combiner 4813 may befashioned as the arrayed waveguide (AWG) shown and described relative toFIG. 34 configured as a multiplexer. The programmable delayed generators4814 and 4816 may be fashioned as the embodiment of programmable delaygenerator 4200 shown and described relative to FIG. 42.

During operation, light travelling down the transmission fiber 4802 maybe formed from a plurality of temporarily spaced data bits, with eachdata bit having a P polarization and an S polarization. The temporalseparation between a first polarization and a second polarization mayseparate from a distance shown as d to a distance shown as d′.Approximately every couple thousand miles, or as determined suitable forthat particular transmission system, one polarization controller 4800can be located within the transmission system to limit any adverseoverlapping of polarizations.

The polarization controller 4800 acts to adjust the temporal spacing ofeach signal, and therefor limits the potential that the time betweenadjacent polarizations from adjacent signals is reduced to thepolarizations are in danger of overlapping. As such, as the opticalsignal is received at the output 4804 of the transmission fiber 4802, itencounters the polarizer 4806 that separates the polarized signals.After the polarized signals are cleanly separated, the signal continueson to the beamsplitter. The beamsplitter 4808 splits the signal into twopolarizations, such that a first polarization follows the first path4810 and the second polarization follows a second path 4812. Theprogrammable delay generators 4814 and 4816 are included respectively inthe first path 4810 and the second path 4812 to temporally space therespective first polarization (of the P or S variety) and the secondpolarization (of the opposed variety) by a desired and controllableperiod. Providing a temporal delay in the suitable programmable delaygenerator 4814, 4816 allows the controller 201 to adjust the temporalspacing between the P polarization and the S polarization by aprescribed time period, as dictated by the operating conditions of thenetwork. It is common in long data transmission systems to have the Ppolarization and the S polarization temporally separated further apart.The polarization controller 4800 readjusts the time between the Spolarization and the P polarization. As such, the S polarization or theP polarization will not overlap with the polarizations from adjacentsignals.

For a given fiber, each color has its own polarization controller 4800.There might be 80 colors being used in a typical optical fiber, so therehave to be a large number of distinct polarization controllers to handleall the colors in a fiber. A central office for a telephone network maybe terminating a large number of fibers (e.g., 100). As such, a centraloffice may need 8000 polarization controllers at a central office todeal with the dispersion problem on all of their fibers. As such,expense and effectiveness of operation of each polarization controllerare important.

FIG. 50 shows one embodiment of a method 5000 that can performed by thecontroller 201 in maintaining the temporal separation of a firstpolarization and a second polarization between an input optical signaland an output optical system. The method 5000 starts with block 5002 inwhich the controller detects the first temporal separation of a firstpolarization and a second polarization in the output optical signal. Theoutput optical signal may be considered to be that signal which isapplied to the input 4804 in FIG. 48, as referenced by the character d.

The method 5000 continues to block 5004 in which the controller 201compares the first temporal separation of the output optical signal to asecond temporal separation of an input optical signal. The input opticalsignal is that signal which is initially applied to the transmissionfiber, and is indicated by the reference character d in FIG. 48. Thecontroller 201 typically stores, or can determine, the value of thesecond temporal separation between the first polarization and the secondpolarization. For example, a transmitter, or transmission system, thatgenerates the signal using two polarizations may typically provide afixed delay d between all first polarizations and the correspondingsecond polarizations in the input optical signal. Alternatively, thecontroller 201 may sense whether the temporal separation distance d′between first polarization and the second polarization of the outputoptical signal are becoming too far apart. In both cases it is desiredto reduce the second temporal separation.

The method 5000 continues to step 5006 in which the controller 201separates the input optical signal into two paths, indicated as thefirst path 4810 and the second path 4812 in FIG. 48. The separated firstpolarization from the output optical signal is transmitted along thefirst path 4810. The separated second polarization from the outputoptical signal is transmitted along the second path 4812.

The method continues to step 5008 in which the controller, using eitherthe first programmable delay generator 4814 or the second programmabledelay generator 4816 that are located respectively in the first path4810 and the second path 4812, delay the light flowing through theirrespective paths. Such a delay of the light along each respective path4810, 4812 corresponds to the respective first polarization or thesecond polarization travelling through each respective path. Oneembodiment of the delay of the light in the respective programmabledelay generators 4814, 4816 is provided in a similar manner as describedin the embodiments of programmable delay generator 4200 shown in FIGS.42 and 43. The method 5000 continues to block 5010 in which the firstpolarization that travels over the first path 4810 and the secondpolarization that travels over the second path 4812 are combined (andinclude the respective delays for each polarization). Combining thesesignals form an output optical signal having its temporal spacingbetween the first polarization and the second polarization modified.This output optical signal having modified temporal spacing may be inputas an input optical signal to a new length of transmission fiber, or maybe transmitted to the end user.

FIG. 49 shows one embodiment of an interferometer that may beconstructed using optical waveguide devices, including one or moreprogrammable delay generators 4200. The interferometer 4900 (e.g., aMichelson interferometer) comprises a laser 4902, a beamsplitter 4904, afirst programmable delay generator 4906, a second programmable delaygenerator 4908, and an interference detector 4910. In the interferometer4900, one or both of the first programmable delay generator 4906 and thesecond programmable delay generator 4908 must be provided. If only oneof the two programmable delay generators is provided, then a mirror issubstituted at the location of the missing programmable delay generator.

During operation, coherent light is applied from the laser 4902. Thecoherent light, follows path 4920 and encounters the beamsplitter 4904.The beamsplitter splits the coherent light from the laser into to followeither path 4922 or path 4924. Light following path 4922 will encounterthe first programmable delay generator 4906 and will be reflected backtoward the beamsplitter. Light following path 4924 will encounter thesecond programmable delay generator 4908 and will be reflected backtoward the beamsplitter 4904. As a return path of light from travellingalong path 4924 and 4922 encounters the beamsplitter, a certainproportion of the return light following both paths 4924 and 4922 willbe reflected to follow path 4926.

Based upon the position of the first and second programmable delaygenerators 4906, 4908, the light travelling along paths 4922 and 4924will travel a different distance (the distances traveled include theoriginal path and the return path from the programmable delaygenerator). These differences in distances will be indicated by theinterference pattern in the signal following path 4926. Depending on thewavelength of light used in the Michelson interferometer, the Michelsoninterferometer may be used to measure differences in distance betweenpath 4922 and 4924. In one embodiment, one or more of the programmabledelay generator shown as 4906, 4908 is replaced by a mirror or a likedevice. For example, a modified Michelson interferometer may be used asin optical interference topography in which the position of the retina,relative to the eye, is measured to determine the state of the eye. Theretina acts as a mirror, and focuses some of the light out of the eye.Therefore, an interferometer, or more specifically an opticalinterference topography device can detect light reflected off theretina. As such, in the Michelson interferometer, one of theprogrammable delay generators 4906 or 4908 can be replaced by the eye ofthe examined patient. The other one of the programmable delay generators4908, 4906 can be used to measure distances within the eye.

The embodiment of the methods shown in FIGS. 7 and 8 may be used toadjust or calibrate the voltage applied to an electrode of an opticalwaveguide devices based on variations in such parameters as device ageand temperature. These methods rely on such inputs as the temperaturesensor 240 measuring the temperature of the optical waveguide device andthe meter 205 measuring the resistance of the gate electrode, as well asthe controller 201 controlling the operation of the optical waveguidedevice and controlling the methods performed by FIGS. 7 and 8. Themethods may be applied to systems including a large number of opticalwaveguide devices as well as to a single optical waveguide device. Assuch, the optical waveguide system, in general, is highly stable andhighly scalable.

VI. Generalization of Active Optical Devices in SOI

So far, this disclosure has described many embodiments of active devicesin which the 2DEG layer is “patterned” and its strength (i.e. number offree carriers) is modified to achieve various optical functions such asmodulation, deflection, etc.

Other simple electronic devices will also serve the same purpose in SOI.For example, a diode (p-n junction) in forward bias (see FIG. 81) willresult in a large number of free carriers in region 8114 which will thenmodify an optical beam passing through that region. In reverse bias, thefree carriers are removed from the region 8114.

Another example of an electronic device that may not use such a 2DEGlayer is a field plated diode (FIG. 90) where the characteristic of thep-n diode are modified by application of “gate voltage” varying the freecarrier distribution and thus its effect on the optical beam. In thiscase, the gate pattern may be used in a similar manner as in 2DEGstructures. Yet another example is a simple Shottky diode.

In all of the above, changes in the free carrier distribution, withrespect to the electromagnetic field profile in the waveguide will causevarious optical functions to be attained. It is intended that thisdisclosure relate all of these embodiments.

VI. Input/Output Coupling Embodiments

This section describes a variety of embodiments of input/output lightcouplers 112 that may be used to apply light into, or receive lightfrom, a waveguide included in an integrated optical/electronic circuit103. Coupling efficiency of the input/output light couplers 112 is avery important consideration for optical waveguide devices sinceregardless of how effective the design of the various optical waveguidedevices, each optical waveguide device depends on the application oflight into or out of the optical waveguide device using the input/outputlight couplers 112.

There are a considerable number of aspects described herein associatedwith the concept of combining electronic aspects and optical conceptsinto an integrated optical/electronic circuit 103. This sectiondescribes a variety of different operations of, and embodiments of,input/output light couplers 112 included in an integratedoptical/electronic circuit 103. The optical functions may use footprintson the integrated optical/electronic circuit 103 that are not used forelectronics functions, and otherwise represent wasted space in theintegrated optical/electronic circuit 103. The integratedoptical/electronic circuit 103 provides a commonfabrication/manufacturing platform for optics and electronic circuitsand provides common design techniques for building optical andelectronic functions.

FIG. 51 shows a side cross sectional view, and FIG. 52 shows a top view,of one embodiment of the integrated optical/electronic circuit 103including a plurality of input/output light couplers 112 and an on-chipelectronics portion 5101. The on-chip electronics portion 5101 as wellas the plurality of input/output light couplers 112 are mounted relativeto one of the embodiments on a silicon-on-insulator (SOI) slab waveguide5100 as shown in FIGS. 53 to 58. The (SOI) slab waveguide 5100 includesthe substrate 102, the first electrical insulator layer 104, and thewaveguide 106.

Each input/output light coupler 112 includes an evanescent couplingregion 5106 and a light coupling portion 5110. The evanescent couplingregion 5106 is defined using the upper surface of the waveguide 106 andthe lower surface of the light coupling portion 5110. For example, theevanescent coupling configured as a tapered gap portion 5106 may beproduced by an angled lower surface of the light coupling portion 5110.A constant gap 5106 may be produced using a level lower surface of thelight coupling portion 5110. Each input/output light coupler 112 may atany point in time act as either an input coupler, an output coupler, orboth an input and output coupler simultaneously. For those input/outputlight couplers 112 that are acting as an input coupler, the light entersthe light coupling portion 5110, and enters the waveguide 106 throughthe evanescent coupling region 5106. For those input/output lightcouplers 112 that are acting as an output coupler, the light passes fromthe waveguide to the evanescent coupling region 5106, and exits thelight coupling portion 5110.

FIG. 51 illustrates certain optical principles of concern to anintegrated optical/electronic circuit 103 design. The waveguide 106 hasa refractive index of n_(Si) while the light coupling portion 5110formed from silica has a refractive index of n_(i). The angle at whichlight in the light coupling portion 5110 contacts the gap portion 5106is θ_(i). By comparison, the angle at which the light enters thewaveguide 106 is the mode angle, θ_(m). The mode angle θ_(m) varies foreach mode of light traveling within the waveguide. Therefore, if thewaveguide 106 can support one or more waveguide modes, there will be aplurality of mode angles θ_(m1), θ_(m2), and θ_(mx) depending on thenumber of modes. For example, a region of the waveguide 106 in oneembodiment has a height of 0.2μ formed from silicon that is surroundedby the evanescent coupling region 5106 and the first electricalinsulator layer 104 (both of which are formed from glass), supports onlya single TE mode angle θ_(m) of approximately 56 degrees. Therequirements for incident light is that the incident angle θ_(i)satisfies equation 23:n_(i) sin θ_(i)=n_(Si) sin θ_(m)  23where θ_(m) is the mode angle of any particular mode of light.

There are specific requirements for the index of the evanescent couplingregion 5106, also known as the gap region. The refractive index of theevanescent coupling region 5106 has to be very close to that of thewaveguide 106. In general, the upper cladding of the waveguide 106 willbe one of the often-used materials such as glass, polyamide, or otherinsulators used in construction of active electronics. The evanescentcoupling region 5106 may be made from the same material, air, or filledwith a polymer-based adhesive that has a similar refractive index. It isdesired for the waveguide to have very close to the same effective modeindex in the regions adjacent the evanescent coupling region 5106 as inregions remote from the evanescent coupling region 5106.

The purpose of the on-chip electronics portion 5101 is to applyelectricity to any of the desired components adjacent to the waveguide,or to perform other electrical signal processing on the chip. Thison-chip electronics portion 5101 is formed using SOI fabricationtechniques that include such techniques as metal deposition, etching,metalization, masking, ion implantation, and application of photoresist.The on-chip electronics portion 5101 may be formed in a similar manneras typical SOI electronic chips such as used in the CPU for the PowerPC™. The electrical conductors of the on-chip electronics portion 5101form a complex multi-level array of generally horizontally extendingmetallic interconnects 5120 and generally vertically extending vias5121, the latter of which extend between multiple metallic interconnectlayers at different vertical levels. The metallic vias 5121 that extendto the lower surface of the on-chip electronics portion 5101 typicallycontact a metalized portion on the upper surface of the waveguide 106 tocontrollably apply electrical signals thereto. For instance, in theembodiment of optical waveguide device shown in FIG. 2, the electricityapplied via the voltage source 202 and the substantially constantpotential conductor 204 are selectively applied via the electricalconnections comprising a maze of generally vertically extending metallicvias 5121 and generally horizontally extending metallic interconnects5120. The substantially constant potential conductor 204 acts to tie thevoltage level of the first body contact electrode 118 to the voltagelevel of the second body contact electrode 122. Although a particularconfiguration of metallic vias 5121 and horizontally extending metallicinterconnects 5120 within the on-chip electronics portion 5101 is shownin FIG. 51, other configurations of on-chip vias and interconnects arepossible, and are considered within the scope of the present invention.

The electronics portion 5101 may be considered as controlling theoperation of the active optical circuits, as shown, e.g., in FIGS. 1through 5, 9-19, etc. Opto-electric functions can therefore be performedon a single chip, such as a silicon-on-insulator (SOI) type chip. Assuch, planar lithography and/or projection lithography techniques can beused to form the integrated optical/electronic circuits of the presentinvention in a manner wherein optical components (e.g., waveguides andpassive prisms and lens) and electrical components (e.g., transistors,diodes, conductors, contacts, etc.) can be formed and fabricatedsimultaneously on the same substrate. The electrical components can beused to control the function of the electrical devices, or the functionof optical components (e.g., to make a passive optical device intoactive optical device) to perform other signal processing on the chip.

It is envisioned that the levels of silicon layers of the on-chipelectronics portion 5101 are formed simultaneously with the one or morelayers of the evanescent coupling region 5106, (or the gap portion),and/or the light coupling portion 5110 of the input/output light coupler112. In other words, any pair of vertically separated layers on theon-chip electronics portion 5101 may be formed simultaneously with anyportion of optical elements 5106, 5110 that is at substantially the samevertical level using, for example, planar lithography or projectionlithography techniques. Therefore, any one of the one or more layers ofthe evanescent coupling region 5106 and/or the light coupling portion5110 that are at generally the same vertical height as the layers on theelectronics portion 5101 will be formed simultaneously, although thedifferent portions will undergo different doping, masking, ionimplantation, or other processes to provide the desired optical and/orelectronic characteristics. As such, technology, know how, processingtime, and equipment that has been developed relative to the fabricationof electronic circuits (e.g., techniques for fabricating thin SOIsemiconductor chips) can be used to construct optical and electroniccircuits simultaneously on the same substrate.

Different embodiments of the evanescent coupling region 5106 include araised evanescent coupling region, a lowered evanescent coupling region,a lack of an evanescent coupling region 5106, or an angled evanescentcoupling region (an evanescent coupling region is formed with a taperedgap portion 5106, and as such is provided the same reference numbersince they are likely the same structural component). Differentembodiments of the evanescent coupling region 5106 can be formed fromair, an optically clean polymer (that can be configured to act as anadhesive to secure the input/output light coupler 112), or a glass. Itis envisioned that certain embodiments of evanescent coupling region5106 in which light is coupled to, or from, the waveguide 106, have athickness in the order of 0.1μ to 0.5μ. The material of the evanescentcoupling region 5106 can be deposited to its desired thicknesssimultaneously with the deposition of the on-chip electronics portion103.

Certain embodiments of the input/output light coupler 112 include a gapportion 5106 that is tapered, while other embodiments of theinput/output light coupler 112 include a gap portion 5106 that has auniform height thickness. In one embodiment, the gap portion 5106 istapered to support one edge of the light coupling portion 5110 at aheight of less than 100 microns (and typically only a few microns) abovethe other edge of the gap portion 5106. Certain embodiments ofevanescent coupling region 5106 are formed from an optically transparentmaterial that can secure the light coupling portion 5110. Certainembodiments of the evanescent coupling region 5106 include a gap portion5106 while in other embodiments, the gap portion 5106 is missing.Certain embodiments of the gap portion 5106 act to support the lightcoupling portion 5110. Other embodiments of gap portion include adistinct ledge 5502 that is formed during manufacture which supports thelight coupling portion 5110 but only act to suitably direct the lightbeam at a desired mode angle to enter the waveguide 106. Differentembodiments of the light coupling portion 5110 include a prism couplingor a grating portion. It is envisioned that certain embodiments of thelight coupling portion 5110 are formed either from silicon orpolysilicon.

FIGS. 53 to 58 illustrate an exemplary variety of embodiments ofinput/output light coupler 112. In one embodiment of input/output lightcoupler 112, the light coupling portion 5110 (e.g., a prism or gratingformed on a wafer) is formed as a separate portion from the element thatforms the gap portion 5106 as described relative to the embodimentsshown in FIGS. 59 and 60. Additional material may be built-up to allowfor some or all of the built-up material to act as sacrificial materialthat may be partially removed to form, for example, portions of thelight coupling portion 5110. In another embodiment of input/output lightcoupler 112 as described relative to FIG. 56, at least some of thecomponents that form the light coupling portion 5110 are formedsimultaneously with the elements that form the combined gap portion5106. In this disclosure, the term “sacrificial material” generallyrelates to material that is applied during the processing of theintegrated optical/electronic circuit 103, but is not intended to remainin the final integrated optical/electronic circuit 103. The sacrificialmaterial as well as certain portions of the integratedoptical/electronic circuit can be formed from materials well known inthe art such as polysilicon, polyamide, glass, and may be removed usingsuch etching techniques as Chemical Mechanical Polishing (CMP).

In the embodiment of input/output light coupler 112 shown in FIG. 53,the gap portion 5106 formed in the evanescent coupling region 5106 hassubstantially constant thickness. Any light coupling portion 5110 (e.g.,a prism or grating) that is mounted on the gap portion 5106, that has aconstant thickness, and a base that is substantially parallel to thewaveguide 106. The thickness of the evanescent coupling region 5106 isselected to position the base of the light coupling portion 5110relative to the on-chip electronics portion 5101 such as, e.g., at thesame level. Light rays 5120 passing through the embodiment ofinput/output light coupler 112 shown in FIG. 53 must satisfy the basicprinciples described relative to FIG. 51, e.g., equation 23.

The light rays 5120 in each of the embodiments of input/output lightcouplers 112 shown in FIGS. 53 to 58 follow considerably different pathsthrough the different elements to or from the waveguide. The illustratedpaths of the light rays 5120 in each of these embodiments ofinput/output light coupler 112 are intended to be illustrative ofpossible light paths determined as described relative to FIG. 51, andnot limiting in scope.

The embodiment of input/output light coupler 112 shown in FIG. 54 issimilar to the embodiment shown in FIG. 53, except that the evanescentcoupling region 5106 can be formed considerably thinner, etched away, oreven entirely removed. In the embodiment of input/output light coupler112 shown in FIG. 54, the light coupler 112 is mounted directly to thewaveguide 106. Light passing through the embodiment of input/outputlight coupler 112 shown in FIG. 54 must satisfy the basic principlesdescribed relative to FIG. 51, e.g., equation 23.

The embodiment of input/output light coupler 112 shown in FIG. 55includes a ledge 5502 that forms a support base for one edge of thelight coupling portion 5110 (e.g., a prism or grating). The ledge 5502may have thickness that provides the desired angle of the base of theinput/output light coupler 112. The ledge 5502 is preferably formed byremoving sacrificial material at the optical I/O location using anetching process, and the base of the light coupling portion 5110 isangled at a slight angle by resting it on the ledge 5502. In certainembodiments, the height of the ledge 5502 is in the range of under fiftymicrons, and may actually be in the range of one or a couple of microns.The gap portion 5106 may be filled with such optically clear polymer orglass material that provides the desired optical characteristics to thelight entering into, or exiting from, the waveguide. Light rays 5120passing through the embodiment of input/output light coupler 112, shownin the embodiment of FIG. 55, must satisfy the basic principlesdescribed relative to FIG. 51, e.g., equation 23.

The embodiment of input/output light coupler 112 shown in FIG. 56includes a grating 5604 formed on an upper surface of the evanescentcoupling region 5106 that may include a tapered or constant thicknessgap portion 5106. The grating 5604 may be, e.g., a surface gratingformed using the known etching techniques. Light rays 5120 passingthrough the embodiment of input/output light coupler 112 shown in FIG.56 must satisfy the basic principles described relative to FIG. 51,e.g., equation 23. The grating can be replaced in general by adiffraction optical element (DOE) causing both a change in the lightdirection and the spatial extent (e.g., for focusing), to match theexpected spatial profile at the base of the light coupling region 5110.

The embodiment of input/output light coupler 112 shown in FIG. 57includes the ledge 5502 that forms a base for one edge of the lightcoupling portion 5110. The light coupling portion, in this embodiment,includes a wafer 5702 having a grating 5604 formed on an upper surfaceof the wafer. The ledge may be the desired thickness to provide thedesired angle of the light coupling portion, such as in the range ofunder ten microns in certain embodiments. The ledge 5502 is preferablyformed by sacrificial material at the optical I/O location being removedusing an etching process, and the base of the wafer 5702 being angled ata slight angle to rest on the ledge. The region between the base of thelight coupling portion 5110 and the upper surface of the waveguide 106is filled with such taper gap material as an optically clear polymerthat includes an adhesive or a glass. Light rays 5120 passing throughthe embodiment of input/output light coupler 112 shown in FIG. 57 mustsatisfy the basic principles described relative to FIG. 51, e.g.,equation 23.

The embodiment of integrated optical/electronic circuit 103 shown inFIG. 58 further includes a wafer 5820 layered above the electronicsportion 5101 and the evanescent coupling region 5106. The wafer 5820 maybe fabricated as a distinct component that is later combined with theportion of the integrated optical/electronic circuit 103 including theevanescent coupling region 5106 and the electronics portion 5101, oralternatively wafer 5820 may be deposited as an additional layer on topof the portion of the integrated optical/electronic circuit 103including the evanescent coupling region 5106 and the electronicsportion 5101. The wafer 5820 is alternatively formed from semiconductormaterials such as silicon or silica.

The region of the wafer 5820 physically located adjacent and above theevanescent coupling region 5106 acts as the input/output light coupler112. Since the grating 5604 is formed on the upper surface of the lightcoupling portion 5110, light that is applied to the grating will bediffracted within the light coupling portion 5110 to the angle θ_(i),which is then applied to gap portion 5106. Based on the configuration ofthe light coupling portion 5110, the evanescent coupling region 5106,and the waveguide 106, the light applied to the grating 5604 can beapplied at a controllable angle so that the coupling efficiency of thelight input into the input/output light coupler 112 is improvedconsiderably. Light rays 5120 passing through the embodiment ofinput/out light coupler 112 shown in FIG. 58 must satisfy the basicprincipal described relative to FIG. 51, e.g., equation 23.

By viewing the embodiments of input/output light couplers 112 shown inFIGS. 51 to 58, it appears that the light coupling portion 5110 may beapplied as a distinct component as positioned relative to the remainderof the integrated optical/electronic circuit 103. The alignment isnecessary between the light coupling portion 5110 relative to theremainder of the integrated optical/electronic circuit 103 wherediscrete light coupling portions 5110 are used, except in the mostsimple integrated optical/electronic circuits.

This portion of disclosure therefore discloses a different embodiment ofintegrated optical/electronic circuit 103 including discreet lightcoupling portions 5110. The light coupling portions 5110 may befabricated as a distinct component from the remainder of the integratedoptical/electronic circuit 103 or simultaneously with the remainder ofthe integrated optical/electronic circuit 103. In actuality, FIG. 58shows one embodiment of an integrated optical/electronic circuit 103 inwhich all of the material forming the input/output light coupler 112 maybe deposited using such processes as physical vapor deposition (PVD),chemical vapor deposition (CVD), and/or electrochemical deposition.These same processing steps may be used to deposit different layers ofthe integrated optical/electronic circuit. Processes such as CMP areused to planarize the wafer, and various photoresists used incombination with etchants are used to etch patterns.

The application of deposition and etching processes is well known tosuch circuits as SOI circuits including such electronic circuits as theelectronics portion 5101. However, it is further emphasized that thedeposition and layering of the material of the input/output lightcoupler 112 may use similar techniques, in which the opticalcharacteristics of the waveguide and the coupling region are alteredrelative to their neighboring opto-electronic components by selectingdifferent masked configurations as part of a sequence to build theopto-electronic circuit.

Alignment of any input/output light coupler 112 relative to theremainder of the integrated optical/electronic circuit 103 is importantto achieve desired coupling efficiencies. A lateral displacement of theinput/output light coupler 112 relative to the remainder of theintegrated optical/electronic circuit 103 by a distance as small as onemicron may significantly reduce the percentage of light that can becoupled via the input/output light coupler 112 to, or from, thewaveguide 106. Light beams that are applied to the input/output lightcoupler 112 usually can be modeled as a Gaussian-intensity curve incross section. For example, the center of the light beams have astronger intensity than the periphery of the light beams, and theintensity across the width of the light beam varies as a Gaussianfunction.

The characteristics of the optical beam required for best couplingefficiency depends on the nature of the gap portion 5106. Furthermore,the tolerance on the required beam position, beam diameter, and itsintensity distribution also depends on the gap 5106. Tapered gapsgenerally have superior coupling efficiency and are more tolerant tovariations in beam position, diameter, etc. as compared to constantgaps. They are also more suitable to Guassian beams since the expectedoptimum beam profile for optimum efficiency is close to Gaussian.

As light is exiting the output coupler from the waveguide, wherein thewaveguide is carrying substantially uniform intensity of light acrossthe cross-sectional area of the waveguide, it may be desired to onceagain convert the light exiting the output coupler into a light beamthat has a Gaussian intensity profile. Evanescent couplings configuredas a tapered gap portion 5106 as illustrated particularly in FIGS. 55and 57, result in a closer fit to a Gaussian profile than without thetaper gap portion. For example, FIG. 64 shows the calculations for a 0.2micron silicon waveguide formed with the taper. The tapered gap portionis illustrated by line 6402 in FIG. 64, and the height of the taper fromthe waveguide is illustrated along the right ordinate of FIG. 64. Anintensity profile curve 6406 is plotted to indicate the intensityprofile at the base of the input/output light coupling device. Therelative intensity value is plotted as the left ordinate in FIG. 64. Theabscissa measures the distance from a ledge (an arbitrary measuringpoint) in microns. A best fit Gaussian curve 6404 is plotted proximatethe intensity profile 6406, to illustrate how effectively the outputlight from the output coupler models the Gaussian curve. FIG. 65 shows asimilar curve as FIG. 64, except FIG. 65 models a constant thicknessgap, as indicated by the fact that the taper curve 6410 is level in FIG.65. Curve 6412 of FIG. 65 measures the intensity profile for an outputbeam of light that is not Gaussian, but instead exponential.

While it is easy enough to align one or a few input/output lightcouplers 112 relative to their respective integrated optical/electroniccircuit, it is to be understood that in dealing with extremely large andcomplex optical and/or electronic circuits, the alignment is anon-trivial task. Even if it takes a matter of a few seconds to alignany given input/output light coupler 112, considering the large numberof input/output light couplers 112 on any given circuit, manuallyaligning the needed number of input/output light couplers to any oneintegrated optical/electronic circuit 103 may require an extremely largenumber of hours to perform. As such, in order to practically align alarge number of input/output light couplers 112 relative to a relativelycomplex integrated optical/electronic circuit 103, very large scaleintegrated circuits (VLSI) or ultra-large scale integrated circuits(ULSI) processing techniques that are well known in electronic chipcircuit production should be used.

FIGS. 59 to 60 show expanded views of two embodiments of integratedoptical/electronic circuits 103 that each include silicon insulator(SOI) flip chip portion 5904 and an optical/electronic I/O flip chipportion 5902. The SOI flip chip portion 5904 is formed, preferably usingflip chip technology in which the waveguide is preferably a thinwaveguide. It is also envisioned that any substrate, using either SOItechnology or traditionally substrates, is within the scope of thepresent invention. Both of the embodiments of optical electronic I/Oflip chip portions 5902 as shown in FIGS. 59 and 60 include theelectronic portion 5101, as described in FIG. 51. Additionally, eachembodiment of optical/electronic I/O flip chip portions 5902 includes alight coupling portion 5110 and an evanescent coupling region 5106 thatmay be configured as a tapered gap portion or a constant thickness gapportion. In the embodiment of optical/electronic I/O flip chip portion5902 shown in FIG. 59, however, the light coupling portion 5110 isconfigured as a grating 5604, similar to that described relative to,FIGS. 56, 57, and 58.

In the embodiment of optical/electronic I/O flip chip portion 5902 shownin FIG. 60, the light coupling portion 5110 includes a prism. Thegratings shown in the integrated optical/electronic circuit of FIG. 59may be formed using known etching techniques, in which gratings or DOEare formed by etching away thin strips of material. The prisms formed inthe optical/electronic I/O flip chip portion 5902 in FIG. 60 maybeformed using anisotrophic etching. Anisotrophic etching is a knowntechnology by which a crystalline material is etched at different ratesbased on the crystalline orientation of the material. The alignment ofthe crystalline material determines the etch rate. For instance, in ananisotrophic material, the silicon will be etched at a different ratealong the 001 crystalline plane compared to the 010 atomic plane. Suchconfigurations as V-groves and/or angled surfaces can be formed indifferent regions within the optical/electronic I/O flip chip portion5902 using anisotrophic etching.

Both the SOI flip chip portion 5904 and the optical/electronic I/O flipchip portion 5902 may be formed in either the orientation shown in FIGS.59 and 60, or some alternate orientation such as inverted from thatshown in FIGS. 59 and 60. Regions within the embodiments ofoptical/electronic I/O flip chip portions shown in either FIG. 59 or 60as being etched away to form the respective etchings or prisms, may becontrollably formed using masking technology. Masks are used todetermine where photoresist is being applied on the flip chip portion.

Alignment of the various components of the integrated optical/electroniccircuits 103 is provided by proper spacing of the devices. Spacing ofthe devices, as provided by the lithography masking technique, is asignificant advantage of the integrated optical/electronic circuits 103compared to having to align each discrete component. In the embodimentsof integrated optical/electronic circuits 103 shown in FIGS. 59 and 60,a plurality of light coupling portions 5110 are arranged in a patternwithin the optical/electronic I/O flip chip portions 5902. A verticalaxis 5958 may be considered as passing through each light couplingportion 5110. The patterning of the light coupling portions 5110 withinthe optical/electronic I/O flip chip portions 5902 is partially definedby the horizontal distance, indicated by arrow 5960, between each pairof the plurality of vertical axes 5958 on the optical/electronic I/Oflip chip portion 5902. The pattern of the light coupling portions 5110within the optical/electronic I/O flip chip portions 5902 is alsopartially defined by the angle α₁ between all of the arrows 5960 thatextend from any given vertical axis 5958 (the vertical axis defining theposition of one light coupling portions 5110) and all other verticalaxes 5958 located on the optical/electronic I/O flip chip portion 5902.

There is also a patterning of the evanescent coupling regions 5106 onthe SOI flip chip portion 5904 in the embodiments of integratedoptical/electronic circuits 103 shown in FIGS. 59 and 60. To achievesuch patterning on the SOI flip chip portion 5904, consider that avertical axis 5962 may be considered as passing through all of theevanescent coupling regions 5106. The patterning of the evanescentcoupling regions 5106 within the SOI flip chip portion 5904 is partiallydefined by the horizontal distance, indicated by arrow 5964, betweeneach pair of the plurality of vertical axes 5962 on the SOI flip chipportion 5904. The patterning of the evanescent coupling regions 5106within the SOI flip chip portion 5904 is also partially defined by theangle α₂ between all of the arrows 5964 that extend from any givenvertical axis 5962 (the vertical axis defining the position of oneevanescent coupling region 5106) and all other vertical axes 5962located on the SOI flip chip portion 5904.

To allow for alignment in the optical/electronic I/O flip chip portion5902, the patterning (of light coupling portions 5110) on the SOI flipchip portion 5904 matches the patterning (of evanescent coupling regions5106) on the optical/electronic I/O flip chip portions 5902. If thepatterning between the I/O flip chip portion 5902 and theoptical/electronic I/O flip chip portions 5902 match, then alignment isachieved by aligning any two light coupling portions 5110 with any tworespective evanescent coupling regions 5106. Using this type ofalignment, all light coupling portions 5110 on the SOI flip chip portion5904 will be aligned with all evanescent coupling regions 5106 on theoptical/electronic I/O flip chip portions 5902. Securing the SOI flipchip portion 5904 and the optical/electronic I/O flip chip portions 5902in their aligned position allows for a technique of fabricating properlyaligned integrated optical/electronic circuits 103.

The electronic portion 5101 includes a variety of interconnects andvias, depending upon the desired configuration and operation of theintegrated optical/electronic circuit 103. The uppermost layer of theelectronic portion 5101 is in electrical communication with solder balls5930. The solder balls 5930 are used, when inverted, to solder theintegrated optical/electronic circuit 103 to, e.g., a motherboard orsome other printed circuit board to which the integratedoptical/electronic circuit 103 is being secured. The solder balls 5930also provide the electrical connection between the electrical circuitson the printed circuit board and the electrical circuits in theelectronic portion 5101 of the integrated optical/electric circuit 103.

A modulator as described relative to FIG. 1, and the other opticalwaveguide devices may thus be considered as a hybrid active integratedoptical/electronic circuit. The etching and deposition processing can beperformed simultaneously for both the optics portions and the electronicportions. To provide a circuit layout for the integratedoptical/electronics circuit, a radius can initially be drawn around theactive optical circuits and the light coupling portion 5110 to indicatewhere the electronic devices related to the electronics portion 5101 arenot to be located. The electronics can be located everywhere else on theoptical/electronics flip chip portion 5902 that do not conflict with thelight coupling portion 5110 as shown in FIGS. 59 and 60.

In the optical portion of an integrated optical/electronic circuit,photons are made to travel within the different embodiments of opticalwaveguide devices as dictated by the passive optical structure and theeffect of the active optical structures. Active electronic transistorsand other devices such as transistors work by controlling theconcentration of electrons and holes by application of potentials. Thesedevices alter the number of electrons and holes rapidly in a givenregion. This change in the concentration of electrons and holes resultsin the transistor gain as well as the transistor switching action. Inthe active optical regions of the integrated optical/electrical circuit,the photons are made to travel through the same region as where thesefree-carriers are located. Therefore, in the integratedoptical/electrical circuit, electronic actions have a result in theoptics portions of the circuit. The free carriers are used for bothelectronic portions and photonic portions.

In one embodiment, the mask that defines the optic portions (activeand/or passive) and the mask that defines the electronic portions(active and/or passive) are essentially combined in production. In otherwords, without close examination, a person could not be certain as towhether a feature in a mask relates to an electronic or optical portionof the integrated optical/electric circuit. In such an embodiment, therewill be no clear cut delineation between a mask for forming onlyelectronic components or a mask for forming only optical components onthe substrate.

A lens is used to project the shape of a mask onto the photoresist todefine the shapes formed on the substrate during each processing step.The depth of focus (DOF) is an important consideration in projecting thefeatures of the mask. All the features in a mask have to lie within thedepth of focus or they do not print well using a lithographic processsince the feature will be out of focus. Chemical Mechanical Polishing(CMP) has become an important process because following etching ordeposition of silicon, the topography of the upper surface of thesubstrate has minute waves. A second level of metal cannot be imaged onsuch a wavy surface and thus cannot be deposited on the wavy surface.The surface waves can be planarized by CMP. Since a typicalmicroprocessor has six to seven layers of metal, the time necessary toprocess such a device is considerable.

One embodiment of the integrated optical/electronics circuit on thin SOIuses planar lithography manufacturing techniques. The active electronicsare included as waveguides in the silicon level of the integratedoptical/electronic circuit. The metal levels can be deposited in theelectronics portion interspaced with material such as glass or polyamideto fill in the surface irregularities. The interespacing material has tobe leveled before the next metal layer is deposited. This process isrepeated for each layer. With planar lithography, each imagingphotoresist exposure requires a very flat wafer consistent with minimumfeature size and DOF requirements.

Projection lithography is therefore used to project an image onphotoresist which is used to determine the pattern on a wafer such as aSOI wafer. In a typical lithography, the aspect ratio of horizontal tovertical features is preferably close to 1 to 1. The uneven, etchedportions are filled with glass/polyamide, then planarized before thenext photoresist/exposure step. The wafer is absolutely plate-like andhas a very uniform layer of the photoresist, which when exposed withlight etches certain selective regions during planar lithography. Once asubstantially uniform photoresist layer is deposited, the mask is usedto develop a pattern on the wafer. The projection lithography process isrepeated for multiple photolithography cycles to provide the desiredelectronic portion 5101 and optical portion on the wafer.

The general rule of the thumb is that the minimum feature size (MFS) isgiven by equation 24:MFS=(0.6 times λ)/NA  (equation 24)

The 0.6 constant generally replaces the semiconductor constant k1 thatdepends on the quality of the lens and other such factors. The 0.6constant is an approximation for a very strong lens, and is not exact.NA is the numerical aperture of the lens, which is a function of thespeed of the lens. A popular wavelength for such a lens is 248 nm. Theminimum feature size is the smallest size that can be printed usingtraditional lithography. Once the minimum feature size for a given NA isdetermined, the depth of focus can be determined as DOF=λ/(NA)². Theminimum feature size and the depth of focus are therefore fundamentallyrelated.

There are curves that indicate the relationship between the depth offocus and the minimum feature size. Optical scientists have attemptedmany techniques to overcome this relationship. The result of thisrelationship is that when the chip is brought into focus for planarlithography, the entire image has to be in focus.

Building the integrated optical/electrical circuit 103 necessitatesmultiple steps of exposure on photoresist that is layered on theuppermost layer of the substrate. To expose the photoresist, thephotoresist must be initially evenly applied. Spinning the whole waferproduces a substantially uniform layer using centrifugal force. If thereare a variety of big structures, the structures act like little damsthat limit the radially outward flow of the photoresist. Even a rise intopography by 50 nm causes such photoresist build-up problems in thelithography. The photoresist is not going to be uniform following thespinning. As described herein, photoresist must be uniform before it canbe exposed.

FIGS. 63A to 63D, show a process of simultaneously depositing silica,other suitable dielectric, polysilicon, etc. layer on both the lightcoupling portion 5110 and the electronic portion 5101. Initially, asilicon layer 6302 is deposited somewhat uniformly across the entireintegrated optical/electrical circuit 103, including both theelectronics portion 5101 and the light coupling portion 5110. Both theembodiments of the light coupling portion that may include prisms, aswell as gratings, rely upon homogenous build up of silica throughout theentire light coupling portion. By comparison, the electronics portion5101 is formed using a series of silica layers, interspersed withmetallic interconnects through which metallic vias vertically extend.Therefore, a series of additional metalization and other steps arenecessary between successive depositions of silica. By comparison, sincethe light coupling portion is homogenous, relatively little processingwill occur between the various silica deposition steps. In FIG. 63A, thelayer of silicon 6302 is deposited on the upper surface of theintegrated optical/electrical circuit 103 using known silicon depositiontechniques, such as chemical vapor deposition and sputtering.

The planer lithography method continues in FIG. 63B in which aphotoresist layer 6304 is deposited on the upper surface of thedeposited silicon layer 6302. Photoresist may be applied, and then thesubstrate 102 typically spun so that the photoresist layer is extendedunder the influence of centrifugal force to a substantially uniformthickness. In FIG. 63C, the lithography portion 6308 selectively applieslight to the upper surface of the photoresist layer 6304, thereby actingto develop certain regions of the photoresist layer. Depending upon thetype of photoresist, the photoresist may harden either if light isapplied to it, or will not harden if light is not applied. Thelithography portion 6308 includes a lithography light source 6310 and alithography mask 6312.

The lithography mask 6312 includes openings 6314 that define, and arealigned with, those areas of the photoresist layers 6304 at which it isdesired to apply light. The lithography light source 6310 generates thelight in a downwardly, substantially parallel, fashion toward thelithography mask 6312. Those portions of the lithography mask 6312 thathave an opening allow the light to extend to the photoresist layer 6304as shown in FIG. 63C. Applying light from the lithography portion 6308acts to develop certain portions of the photoresist layer 6304.

The photoresist layer 6304 is then washed, in which the undevelopedportions of the photoresist are substantially washed away while thedeveloped portions of the photoresist layer remain as deposited. Thedeveloped, and thereby remaining portions of the photoresist layerthereupon cover the silicon thereby allowing for selected portions ofthe silicon layer to be etched. The etching acts on those uncoveredportions of the silicon layers 6302 that correspond to the undevelopedregions of the photoresist layer. During etching, the developed portionsof the photoresist layer 6304 cover, and protect, the covered portionsof the silicon layer 6302, and protect the covered portions of thesilicon layer 6302 from the etchant. Following the etching, respectivestructures 6350 and 6352 remain that are ultimately used to form part ofthe respective optical (e.g., the input/output light coupler 112) andelectronic (e.g., electronic portion 5101) portions.

The well known process of metal deposition, doping, and selectiveetching is used in the semiconductor processing of electronic devicesand circuits. This disclosure, however, applies innovated circuitprocessing techniques, involving etching and deposition, to opticaldevices and circuits as well as electronic devices and circuits, so bothtypes of devices and circuits can be simultaneously fabricated on thesame substrate.

Processors like the PowerPC require a large number of processing stepsto fabricate. Therefore, a mask is used to define one pattern. Thepattern is developed, then the part is removed. Another part that is tobe doped and anti-doped is used, which requires two different mask sets.One mask set is used to expose the p-type photoresist. The next mask setexposes the n-type photoresist.

Thus, as can be seen from the above description, light coupling regionsare processed along with the remainder of the circuit and specialproperties required in these regions are imparted as part of the circuitbuilt using planar lithography techniques.

VIII. Hybrid Active Electronic and Optical Circuits

This portion of the disclosure concerns the operation of and fabricationof hybrid active electronic and optical circuits. Passive opticalcircuits are considered those optical circuits in which thecharacteristics of light flowing through it are determined duringfabrication. By comparison, the active electronic components are thosecomponents whose characteristics change by application of potentials atits terminals. Active optical elements are essentially analogous toactive electronic components except that photons are allowed to passthrough the active optical elements to achieve optical functions as hasbeen described relative to e.g., FIGS. 1-5, and 9-49. For example,diodes, transistors, and the like are examples of active electroniccomponents. In this disclosure, each layer of active electroniccomponents is formed simultaneously as a simultaneous layer of opticalcomponents formed on the same hybrid active electronic and opticalcircuit. As such, certain embodiments of hybrid active electronic andoptical circuits are integrated optical/electronic circuits, and viceversa. Note that an optical circuit may include a combination of activeand passive portions, in a similar manner that an electronic circuit mayconsist of active components such as a diode and a transistor andpassive components such as a resistor.

FIG. 66 shows one embodiment of hybrid active electronic and opticalcircuit 6502. The hybrid active electronic and optical circuit 6502includes an active electronic component 6504 and a passive opticalcomponent 6506. The passive optical portion 6506 includes aninput/output light coupler 112 (not shown), light mirror of 6508, inputregion 6507, an output region 6510, and a channel portion 6512 thatconnects the input region 6507 to the output region 6510. The lightmirror 6508 directs light input from the input/output light coupler 112to the throat 6514 of the channel portion 6512. In an alternateembodiment, throat 6514 need not be tapered, and the configuration ofthe other components shown may be changed in any manner that allowslight to efficiently pass through channel 6512. Light that is applied bythe input/output light coupler 112 travels in a parallel directionwithin the input region 6507 until it reaches the light mirror 6508.Thereupon, the light mirror 6508 directs all reflective light toward thethroat portion 6514. As such, one embodiment of the light mirror 6508 issuitably aligned to reflect as much light as possible towards the throat6514.

Light follows through the channel portion 6512 in a manner to be actedupon by any desired active opto-electronic portion 6504. After the lighthas exited the channel portion 6512, light enters the output region 6510and is directed toward the light mirror 6508 that is located in theoutput region 6510. Light directed toward the light mirror 6508 from thechannel portion 6512 is reflected toward the input/output light coupler112 in optical communication with the output region 6510. In oneembodiment, the components in a configuration associated with the inputregion 6507 are mirrored by the components and configuration of theoutput region 6510. For example, the light mirror 6508 can be designedas having an identical inverse curvature in the output region 6510 fromthe input region 6507. Similarly, the input/output light couplers 112may be structurally and operationally identical between the input region6507 and the output region 6510. In actuality, the use of the term inputand output is arbitrary, since either the input side can be used eitherfor input or output, simultaneously or non-simultaneously, and theoutput can be used for either input or output, simultaneously ornon-simultaneously. The combination of the input region 6507, lightmirror 6508, the channel portion 6512, and the output region 6510 maybereferred to as a J-Coupler, whose name is derived from the direction oftravel of light within the device.

The active electronics portion 6504 may include a modulator, adeflector, a diode, a transistor, or any other electronic circuit inwhich electricity can be selectively applied to a region outside of thechanneled portion 6512 to control the electromagnetic state of thecircuit or device. The passive optical portion 6506 and the activeelectronic portion 6504 can be fabricated simultaneously to form for anygiven processing layer the hybrid active electronic and optical circuit6502. A large variety of confinement structures and waveguide mirrorscan be produced utilizing concepts disclosed in hybrid electronic andpassive optical circuit 6502. The hybrid active electronic and opticalcircuit 6502 represents one embodiment of the integratedoptical/electronics device. A list of passive optical elements includes,but is not limited to, lens, lenses, mirrors, two dimensional evanescentcouplers, beam splitters, Echelle gratings, grating structures, twodimensional adiabatic taper structures (thin film analog structures).Passive waveguide portions are defined by geometrically patterning thesilicon layer to modify the local effective mode index of the slabwaveguide. In some embodiments, portions of the waveguide layer in thesilicon-on-insulator (SOI) devices are completely removed, and replacedby some material such as glass, polyamide, or polysilicon to producetotal internal reflection so light is contained in a region of thewaveguide. Partial removal or addition of other materials includingpolysilicon is used to define optical properties within the waveguide.

All modifications to the passive waveguide elements are carried out by aset of math using well understood silicon processing steps (e.g., SOIprocessing). In one embodiment, the channel portion 6512 can be anactive optical portion for, e.g., modulation or detection. The lightmirror 6508 may be configured as an off-axis paraboloid or any other oneof a variety of shapes that are generally known and described relativeto the optical mirror arts. Additionally, certain mirrors can beconfigured as beamsplitters to separate a single incident beam into aplurality of output beams that can each be directed to an individualport, detector, or other device.

FIG. 68 shows a side view of the hybrid active electronic and opticalcircuit 6502 such as shown in FIG. 66, during processing. The hybridactive electronic and optical circuit 6502 is formed on top of an SOIwafer 6600. The SOI wafer 6600 is initially formed with a planar uppersurface. A photoresist layer 6804 is initially applied to the uppersurface of the SOI wafer 6600. A photolithography mask is applied to theupper surface of the SOI wafer 6600 and the light is applied to thephotolithography mask.

The purpose of the etching process using photolithography is to removenecessary portions of the upper most silicon layer in order to providefunction of the passive optical component 6506, the active electronicsportion 6504, the other electronic components 6602, and the otheroptical components 6604. The shape of the active electronic portion6504, the other electronic components 6602, and the other opticalcomponents 6604 are shown in FIG. 66.

It is also envisioned that portions of the active electronic portion6504, the other electronic component 6602, and the other opticalcomponent 6604 as well as a passive optical component 6506 can beetched, as desired, to provide the desired circuit. Additionally, theportions 6504, 6506, 6604, and 6602 can be partially etched, to a lowersurface in the original upper surface of the silicon layer on the SOIwafer 6600. As such, the etched portions of the silicon layer of the SOIwafer 6600 are shown by the cross-hatching in FIG. 66.

Following the etching of the upper silicon layer of the SOI wafer 6600,its portion is refilled using a glass or a polysilicon materialdeposited in the etched portion. Again, this is important forplanarization so that the glass layer or polysilicon is at substantiallythe same level as the non-etched portions, including the passive opticalcomponent 6506, the active electronic portion 6504, other opticalcomponent 6604, and other electronic component 6606. The use of glass,polysilicon, or polyamide is selected based on optical insulation andother material characteristics.

The light that is traveling within the passive optical portion 6506 thatcontacts a boundary of the input region 6507 or output region 6510 ofthe passive optical component 6506 will experience total internalreflection. The boundaries at which total internal reflection occursinclude the sidewalls of the input region 6507, the output region 6510,and the channel 6512. The boundaries at which total internal reflectionoccurs also includes the insulator layers (such as glass, polyamide,polysilicon, etc.) that are layered above and below the layer of the SOIwafer 6600 on which the passive optical component 6506 is formed. Thistotal internal reflection is utilized by the light mirrors 6508,included in the input region 6507 and the output region 6510, to providetheir refectory characteristics. Total internal reflection is also usedby the channel portion 6512 that is configured to act as a waveguide tomaintain the light traveling therein within a relatively narrow region.

Following the deposition of the glass and/or polysilicon on the etchedportions of the silicon layer of the SOI wafer 6600, the upper surfaceof the glass or polysilicon may be planarized to limit any waviness orsurface irregularities that form therein. Following the planarization ofthe surface, another layer of polysilicon, polyamide, or glass may bedeposited on the upper silicon/glass layer on the SOI wafer 6600. Theother layers consisting of polysilicon, glass, polyamide, and/or anyother material may be used to construct optical circuit elements sincethe waveguide properties are altered by the presence or absence of thesematerials.

FIG. 67 shows one embodiment of a mask 6702 as used during the processof anisotrophic etching. The mask 6702 includes one or more recesses6704 formed in a masked body 6706. The mask 6702 can be used to formoptical I/O ports such as prisms 6010, shown in the optical/electronicI/O flip chip portion 5902 in FIG. 60, from KOH etching. The photoresistlayer 6804 is substantially uniformly applied to the upper surface ofthe silicon substrate 6802 as shown in FIG. 68A. In FIG. 68B, the mask6702 is maintained over, and proximate, the photoresist layer 6804, anda lithography light source 6806 applies light above the mask 6702. Thephotoresist 6804 in this embodiment is a negative photoresist and, assuch, light being applied by the lithography light source 6806 upon aregion of photoresist will not tend to harden the photoresist, but bycomparison, the darkened region of the photoresist covered by portion ofthe mask 6702 will develop.

Following the lithography process shown in FIG. 68B, the siliconsubstrate 6802 is washed, thereby removing the undeveloped etching fromthe upper surface of the silicon substrate 6802 while allowing thosedeveloped regions 6810 of the photoresist to remain on the upper surfaceof the silicon substrate 6802. The anisotrophic etchant 6812 is thenapplied to the upper surface of the etchant, and due to knownanisotrophic etching principles, the silicon substrate will etch atfaster rates along certain crystalline planes than others.

More particularly, the silicon substrate can be maintained in agenerally known manner to etch the silicon substrate 6802 to formbeveled cases 6814 in the silicon substrate 6802. The silicon substratecan continue to be etched as much as desired, perhaps leaving aconnecting portion 6816 between the beveled faces 6814. Thisanisotrophic etching process as shown in FIGS. 68A to 68D can beperformed on a large variety of silicon substrates to form prisms,gratings and other such devices in silica and/or silicon. A large numberof prisms with (or without), can be produced using anisotrophic etching.Anisotrophic etching is an affordable technique to produce a largenumber of prisms. Anisotrophic etching will not produce prisms havingthe traditional 45-45-90 degree cross-sectional prism configuration. Bycomparison, anisotrophic etching produces prisms that have closer to60-30-90 degree cross-sectional prism configuration. The use of suchanisotropically-etched prisms is effective in virtually all knownapplications, but certain users may prefer to use a cut and polishtechnique to produce 45-45-90 degree cross-sectional prisms.

The known cut and polish technique that is used to form prisms may bemore costly and require more time than anisotropically etched prisms.There are therefore a large variety of techniques that can be used toproduce prisms that each have certain benefits and disadvantages. Thedescription of anisotrophic etching and cut and polish is not intendedto be limiting, and any etching technique that provides prisms,gratings, or other input/output light couplers is within the intendedscope of the invention.

To form an integrated optical/electronic circuit, the electronic portioncan initially be formed in the substrate using known processingtechniques. In one embodiment, the substrate being processed can be anSO substrate. The electronics portion is formed in the substrate.Following the formation of the electronics portion, the electronicsportion can be coated with the hardened photoresist as shown in FIG.68C, and the other portions of the silicon substrate in which it is notdesired to anisotropically etch can be similarly coated with thehardened photoresist. The only region remaining on the coated surfacethat is not coated with the hardened photoresist therefore defines thoseregions that will be etched to form the prism or other device. Gratingscan also be formed using anisotrophic etching, however the masks used toform gratings may need finer resolution than those used to etch theprisms.

One advantage of the silicon substrate being etched in a manner with thebeveled faces is shown in FIG. 68D is that since connecting portion 6816may be relatively thin, a fair amount of flexibility may be provided bythe connecting portions. Therefore, force can be applied similar to theprism surface, in a generally lateral direction, in a manner that woulddeform the connecting portions to angle the beveled face somewhat fromits flat configuration. Such angling of the beveled faces associatedwith the prisms have the same result as providing a tapered gapunderneath the prism. The tapered gap can then be filled with someoptically clear material that hardens to maintain a tapered gap. In analternate embodiment, the pressure can be maintained on the prism itselfto maintain the tapered gap.

In alternate embodiment, the thickness of the connecting portions 6816can be increased. For example, an entire wafer or substrate can beformed using such anisotropical etching techniques with only an upperregion of the wafer or substrate being etched. The lower portion, forexample, can include electronic components that might, or might not,relate to the optical device associated with the input/output lightcouplers.

The alignment techniques described above relative to FIGS. 59 and 60(where the patterning of the light coupling portions 5110 on the SOIflip chip portion 5904 matches the patterning of evanescent couplingregions 5106 on the optical/electronic I/O flip chip portions 5902) mayutilize the etched device as shown in FIG. 68D. Masks that define thespacing, and angles, between the plurality of light coupling portions5110 on the SOI flip chip portion 5904 provides the patterning thereof.It is also emphasized that the etching can be performed on the uppersurface of a single substrate including the evanescent coupling regions5106. As such, the light coupling portion 5110 and the SOI flip chipportion 5904 can be formed on a single substrate, with each respectivelight coupling portions 5110 being aligned relative to each respectiveevanescent coupling regions 5106. It is further emphasized that theetching processes used to etch such an aligned hybrid active electronicand optical circuits 6502 and/or integrated optical/electronic circuits103 may include anisotropic etching, cut and polish etching, and anyother type of etching that may be used to etch prisms, gratings, andother light coupling portions 5110.

FIGS. 69, 70, and 71 show three other embodiments of hybrid activeelectronic and optical circuits 6502. FIGS. 69, 70, and 71 are each topviews of their respective devices. The basic purpose of each of thehybrid active electronic and optical circuits 6502 shown in FIGS. 69,70, and 71 is to couple light into a waveguide 6904. The tapered gapregion is used to evanescently couple light into waveguide 6904. Thethree FIGS. 69, 70, and 71 show three different techniques to accomplishthe task of changing the direction of incident light to an anglesuitable for evanescent coupling. These angles can be computed usingcomputational tools such as FDTD.

In the embodiment of FIG. 69, deviation is due to a grating beingintegrated into the Si layer during manufacture. In the case of FIG. 70,a waveguide prism created by altering the effective mode index in theshape of a prism is created. In the embodiment of FIG. 71, a waveguidelens in used. The waveguide 6904 may contain an active optical device.

During (or before/after) the deposition of the desired silicon andelectrical insulators in the active electronic portion 6504, the opticalinsulator materials are deposited in the insulator strip 6906 a and 6906b. Similarly, the etching of the silicon material for, and deposition ofthe desired material to form, the active electronic portion 6504 canoccur simultaneously with the corresponding etching and deposition ofthe materials to form the passive optical portion 6506. The waveguide6904 may additionally be considered as a passive optical portion.

The embodiment of hybrid active electronic and optical circuit 6502shown in FIG. 69 includes a waveguide grating 6902 to couple impinginglight to the waveguide 6904. The waveguide grating 6902 is configuredsuch that impinging light 6920 is deflected at a suitable angle so thedeflected light 6922 enters the waveguide 6904 at a suitable mode angleθ_(M). The waveguide grating 6902 is a passive optical portion 6506, andcan be controlled by active electronics 6504 to control the angle ofdeflection, as described herein. Alternatively, the waveguide grating6902 can be configured as a purely passive device that deflects thelight being applied to the waveguide 6904 to the mode angle.

FIG. 70 shows another embodiment of hybrid active electronic and opticalcircuit 6502 as shown in FIG. 69, except that the waveguide prism 7002has been incorporated in place of the waveguide grating 6902. Similarly,the waveguide prism 7002 is a passive device, that deflects the lightbeing applied to the waveguide 6904 in a mode angle θ_(M). The use ofthe active electronic component 6504 allows adjustability of the lightflowing through the waveguide prism 7002, thereby allowing light flowingthrough the waveguide prism 7002 to be controllably directed at adesired controllable angle to the waveguide 6904.

The material of the waveguide prism 7002, the active electronic portion6504, and the insulator strip 6906 a and 6906 b can all be etched, andthe corresponding layers deposited, simultaneously. Differentphotoresist and masks may allow different materials to be deposited ineach of the areas being etched, however, a sequence of all thedeposition steps and etching steps that comprise all the processesperformed on all of the optical portions and electronic portions, may beperformed simultaneously. If a specific material is being deposited onone portion (but not another), or etched on one portion (but notanother), then the corresponding masks and etching or deposition toolswill be configured accordingly. FIG. 71 shows another embodiment ofhybrid active electronic and optical circuit 6502 in which fullwaveguide lens 7102 is formed in the upper most silicon layer of the SOIwafer 6600 in place of the waveguide prism 7002 shown in the embodimentof FIG. 70.

FIG. 72 shows a top view of another embodiment of hybrid activeelectronic and optical circuit 6502 as formed on the silicon layer 6601of an SOI wafer 6600 which acts as an adiabatic taper 7204. Theadiabatic taper 7204 includes in the silicon layer 6601 a taperwaveguide 7206, a taper insulator 7208, and an outer portion 7210. Outerportion 7210 represents silicon on which other devices can be formed.The taper insulator 7208 can be formed by initially etching away aconsiderable portion of the silicon located between the taper waveguides7206 and the outer portion 7210, and depositing the glass or polysiliconinsulator material defining the taper insulator 7208 therein. The taperinsulator 7208 is positioned adjacent to taper waveguide 7206 whichresults in total internal reflection of light traveling within the taperwaveguide 7206. The input/output light coupler 112 may be a prism,grating, or other coupling device which inputs light into the taperwaveguide 7206. Light within the taper waveguide 7206 is channeled downinto the channel portions 7220. As such, the adiabatic taper isconfigured to reduce the cross-sectional width of the waveguide in whichlight is passing. FIGS. 73 and 74 show two other embodiments of hybridactive electronic and optical circuits 6502. FIG. 73 shows oneembodiment of simple Fabry-Perot cavity 7302. FIG. 74 shows anotherembodiment of coupled Fabry-Perot cavity 7402.

The Fabry-Perot cavity 7302 as shown in FIG. 73 represents anotherhybrid active electronic and optical circuit that may be formed on thesilicon layer or an SOI wafer, and includes a plurality of passiveoptical portions 6506 and an active opto-electronic portion 6504. Thepassive optical portion 6506 includes a waveguide 7310 and a pluralityof gratings 7312. The gratings 7312 may be configured in a similarmanner as Bragg gratings, surface gratings, or other known types ofgratings. This Fabry-Perot waveguide operates similar to the wellunderstood Fabry-Perot cavities used in optics. The reflectivity ofmirrors (in this embodiment, the gratings act as mirrors) and the cavityoptical length determine the reflection/transmission profile of thedevice.

A constructed Fabry-Perot cavity of this type resonates at specificwavelengths as given by equation 25:2dn _(eff)+φ_(mirrors) =mλ  (equation 25)Where D is the cavity length, n_(eff) is the effective mode index of thewaveguide 7310, and φ_(mirrors) is the phase shift on reflection. Theactive electronic portion 6504 maybe considered as an active electroniccircuit, such as a MOSCAP, MOSFET, etc. that is used to change theoptical characteristic of a cavity by changing the effective mode indexwithin the waveguide. Thus, the Fabry-Perot cavity can be switchedbetween different operating states by controlling the voltage applied tothe active electronic portion.

Multiple simple Fabry-Perot cavities 7302 may be axially spaced along asingle waveguide 7310 to form a coupled Fabry-Perot cavity 7402 as shownin FIG. 74. The coupled Fabry-Perot cavities 7402 may be considered as aplurality of simple Fabry-Perot cavities 7302 that are axially aligned,in order to use specific optical characteristics gained by coupling thecavities such as narrow transmission resonances inside a broad bandreflector. The Fabry-Perot structure in this embodiment is used as anactive optical device where the characteristic of the entire structureis controlled by application of potential and change in free-carriers.

A cross section of one of the embodiments of gratings 7304 is shown inFIG. 75. The gratings 7304 include a plurality of raised lands 7502interspaced with plurality of lower lands 7504 to extend along a topsurface of the waveguide 7310. The area within the waveguide 7310 justbelow the raised lands has a greater effective mode index than the areawithin the waveguide underneath the lower lands 7504. As such, thisregularly repeating pattern of changing effective mode index within thewaveguide 7310 acts to reflect a portion of the light that is travellingwithin the waveguide 7310. The reflectivity and wavelength response isgoverned by the magnitude of the change in the effective mode index,spacings, and number of lines. Many methods, such as Finite DifferenceTime Domain (FDTD), exist to compute the reflection/transmissionspectrum of such a structure. Thus, the repeating pattern acts as amirror for the Fabry-Perot cavity, but may be used as a waveguide mirrorin its own right. For example, such a mirror may be used with a specialcurvature instead of the mirror shown in FIG. 66.

The embodiment of grating 7304 shown in FIG. 75 is a passive device. Inthe Fabry-Perot cavity 7302 and the coupled Fabry-Perot cavity 7402shown respectively in FIGS. 73 and 74, the respective activeopto-electric portion 6504 is positioned between adjacent gratings 7304.It may be desired to provide a grating structure that is an activedevice. As such, the wavelengths of light that each grating couldreflect or deflect could be controlled. FIGS. 77 and 76 show twoalternate embodiments of active gratings 7602. The embodiments ofgratings 7602 shown in FIGS. 76 and 77 thus are configured as hybridactive electronic and optical circuits 6502.

The active electronic portion 6504 in the gratings 7602 shown on FIG. 76is provided by providing electrical conductive layer on the uppersurface of the raised lands 7502. By comparison, in the embodiment ofgratings 7602 shown in FIG. 77, the active electronic portion 6504 isprovided by a metalized surface on the lowered lands 7504. By applyingelectric current to the active electronic portion 6504 in the embodimentof gratings 7602 shown in FIGS. 76 and 77, the respective regions withinthe active electronic portion 6504 will change their effective modeindex. By varying the polarity and voltage or current applied to theactive electronic portion 6504, the effective mode index of the regionsunderneath the active electronic portions 6504 can be controlled.

Fabricating the embodiments of gratings 7602 in the embodiments shown inFIG. 76 or 77 that include the active electronic portion 6504 and thepassive optical portion 6506 can be performed using a variety oftechniques. In one embodiment, the material of the gratings 7602 formedabove the level of the lower lands 7504 can be deposited on the upperlayer 6601 of the SOI wafer 6600 to build the gratings up to the levelof the raised lands 7502. In an alternative embodiment, the materialbetween the alternating gratings 7602 can be etched away to form theregions of the gratings that extend from the level of the raised landsdown to the level of the lowered lands 7504. In either of theseconfigurations, the metal layer forming the active electronic portion6504 can be added to the raised lands 7502 or the lowered lands 7504 atthe time of fabrication when the gratings are being formed. The material7620 in the embodiment of gratings 7602 shown in FIG. 76 is preferablyadded on top of the upper layers 6601 of the SOI wafer 6600.

The upper silicon layer 6601 can be built up to the height equal to theraised lands 7502. Following this uniform build up of the upper siliconlayer 6601, a uniform metalization layer can be applied across theentire upper surface of the upper silicon layer. At this time, the uppersilicon layer will be thickened by the addition of silicon, and coatedby a metal layer corresponding to the active electronic portion 6504.Those portions of the upper layers 6601 that do not correspond to theraised lands 7502 can have the upper middle layer etched away usingknown metal etching techniques. Following the etching away of the middlelayer, the region of the upper silicon layers 6601 that are not coatedby the remaining portions of the etched metal, i.e., the silicon areascorresponding to the lowered lands 7504, can be etched away using knownsilicon etching techniques. The etching of both the metal areas and thesilicon layers utilizes masks that have openings, the regions of theopenings corresponding either to the areas that are going to be etchedor the areas that are not going to be etched.

In those embodiments of gratings 7602 in which silicon material 7620 isnot added to the original upper silicon layer 6601, a metalized layer isadded to the upper surface of the upper silicon layer 6601. The depth ofthe metal layer corresponds to the desired depth of the activeelectronic portion 6504. The techniques of etching away the metal layerof the active electronic portion 6504 and the underlying sacrificialsilicon material of the upper silicon layer 6601 are similar to thatdescribed with respect to the removal of the metal and silicon portionswhere silicon has been added.

To fabricate the embodiment of the grating 7602 shown in FIG. 77, theentire upper silicon layer 6601 is built up to the desired height of theraised lands 7502. If the upper silicon layers are higher than thedesired height of the raised lands 7502, then the entire upper siliconlayer is etched uniformly down to the level of the raised lands 7502.Following the etching or metal deposition, it may be necessary to levelthe upper surface of the upper silicon layers using such means as, e.g.,a chemical, mechanical polisher (CMP). Following the CMP processing, aphotoresist is added to the upper surface of the upper silicon layer6601.

Masks are used to define which area, depending upon the type ofphotoresist, are going to be etched away and light is applied throughthe apertures in the masks to the upper surface of the upper siliconlayer 6601 to develop the photoresist, if necessary, to define whichregions will be etched. Etching is then performed on the uncoveredportions of the upper surface of the upper silicon layer 6601, untilthose uncovered portions are lowered to the level to the lower lands7504. The upper surface of the lower lands 7504 are then coated with themetal layer corresponding to the active electronic portion 6504 of thegrating. The deposition of the metal on the upper surface of the lowerlands 7504 can be performed using a mask whose opening corresponds tothe regions of the upper silicon layers 6601 that have been etched downto the lower lands 7504.

FIG. 78 discloses an embodiment of a wavelength division multiplexermodulator 7802 that includes active gratings such as depicted in FIGS.20, 21, and 22. Light, of several wavelengths, is inputted into anactive chirped grating region 7806. Depending upon the state of each ofthe gratings 7602 in the active chirped grating region 7806, wavelengthscorresponding to each grating may be allowed to continue along the paththrough the active chirp grating region 7806 as modulated data on output7810. Alternatively, if any of the gratings 7602 are actuated in theactive chirped grating regions 7806, then corresponding wavelengths oflight will be deflected across a deflection region 7812, and willthereupon enter in passive chirped grating region 7814.

The active chirped grating region 7806 is a hybrid active electronic andoptical circuit 6502 and may include another type of grating such asthat shown in either FIG. 76 or 77. The passive chirped grating region7814, by comparison, does not require any active components, and mayinclude a plurality of the gratings shown in the embodiments in FIG. 75.Gratings can act to receive light, and thereby apply the light to awaveguide, as well as to deflect a light from a waveguide. In analternate embodiment, the active chirped grating region 7806 may beformed from a plurality of the active wavelength specific gratingstructures as shown in FIG. 41. The active grating region 7806 iscreated by patterning the free carrier concentration in the waveguide bythe application of electricity to the grating, depending upon thespecific configuration of the active grating region 7806. The passivechirped grating region 7814 is created at the time of manufacturing bypatterning the waveguide, and is configured to receive light at specificmode angles θ_(M). Gratings can be applied to those waveguides thatreceive light as well as those waveguides that emit light.

FIG. 78 shows two gratings of the active chirped gratings regions 7806being actuated, thereby diverting optical signals having wavelengths λ₁and λ₅ to the passive chirped grating region 7814. Light havingdifferent wavelengths can thus be used to contain distinct datatransmitted as optical signals. Data signals from the data electronicinput portion 7816 may be applied to control the individual componentsof the active chirped grating region 7806. The data electronic inputportion 7816 can be fabricated at the same time, on the chip, as theactive electronic portions 6504 and the passive optical portion 6502shown in the embodiments of FIGS. 76, 77 and 75 respectively. As such,the embodiment of wavelength division multiplexer modulator 7802 shownin FIG. 78 can be considered as an embodiment of hybrid activeelectronic and optical circuit 7602.

FIG. 79 shows an alternate embodiment of wavelength division multiplexermodulator 7902. The embodiment of wavelength division multiplexermodulator 7902 in FIG. 79 includes an input light portion 7903, anoutput light portion 7905, and a plurality of evanescent couplers 7906that optically couple light from the input light portion 7903 to theoutput light portion 7905. The embodiment of FIG. 79, as well as theembodiments in FIGS. 69 to 71, represent an illustrative, but notexhaustive, group of optical devices. The input light portion 7903includes a plurality of gratings 7904, configured to deflect light totheir respective evanescent couplers 7906. The evanescent couplers 7906each are configured as hybrid active electronic and optical circuits6502 since they include a plurality of tapered gap regions 7920 and anactive electronic portion 7922. The tapered gap region may be configuredas embodiments of the hybrid active electronic and optical circuitsshown in FIGS. 69, 70, and 71. As such, depending upon the data appliedfrom the data of electronic input portion to each respective evanescentcouplers 7906, optical beams input to wavelength division multiplexermodulator 7902 will either continue to the grating 7904 located in theoutput light portion 7905, or alternatively, the optical beam will bereflected by the evanescent coupler 7906, and return to the grating onthe input light portion 7903. Only the light portion that continues tothe gratings 7904 located in the output light portion 7905 is includedas modulated data 7920.

The passive optical portion 6506 as well as the active electronicportion 6504 of each evanescent coupler 7906 can be formedsimultaneously on the upper silicon layer 7922 of the SOI wafer 6600.The etching, deposition, and metalization processes can be performedusing similar steps to form all of the passive optical, active optical,passive electronic, and active electronic circuits in the upper siliconlayer 7922 of the SOI wafer 6600.

FIG. 80 shows another embodiment of wavelength division multiplexermodulator 8002. The wavelength division multiplexer modulator 8002includes an input lens 8004, an input Echelle grating 8006, a modulatorarray 8008, and electronics and data portion 8010, an output Echellegrating 8012, and an output lens 8014. The input lens 8004, the inputEchelle grating 8006, the output Echelle grating 8012, and the outputlens 8014 are each configured alternatively as a passive device or anactive device. For example, the lens and Echelle gratings can each beformed by shaping a pattern in the upper surface of the silicon layerdefining the waveguide that alters the effective mode index in theregion of the waveguide under the shaped pattern. Additionally, anembodiment of Echelle gratings 8006, 8012 can be formed as an activedevice as shown in FIG. 25B.

Additionally, in one embodiment, the lenses 8004, 8014 can be configuredas active devices as shown in FIG. 28 or 30. Additionally, the modulatorarray 8008 is configured to block the frequencies that are not going tobe in the modulated output, while allowing those frequencies that arewithin the modulated output to pass to the output Echelle grating 8012.All of the elements 8004, 8006, 8008, 8010, 8012, and 8014 can be formedusing planar lithography techniques using a series of masking steps onthe SOI substrate, as described above. The wavelength divisionmultiplexer therefore has passive waveguide elements, traditionalelectronics, and active waveguide elements formed on the same substrate.

FIG. 81 shows another embodiment of hybrid active electronic and opticalcircuit 6502 that is configured either as a diode or as a field effecttransistor. The field effect transistor 8101 is configured with thesource contact 8102, a drain contact 8104, and a gate contact 8106.Underneath the source contact 8102, there is a P⁺ region 8108 that isbiased by electric voltage being applied to the source 8102. Underneaththe drain 8104, there is a N⁺ region 8110 that is biased by a voltageapplied to the drain 8104. Underneath the gate 8106, there is a loadedoptical structure 8112, and below the loaded optical structure 8112there is a P region 8114. Light beams are modulated by passing currentvia the source 8102 and the drain 8104 through a p-n junctionestablished in the diode. Thus, free carriers from the injected currentare used to change the effective mode index in the loaded opticalstructure 8112 and the P region 8114, that together acts as a waveguide.The phase and/or amplitude of light in the waveguide can thus be variedbased on the applied voltage. An electrical conductor 8120 iselectrically coupled to source 8102. An electrical conductor 8122 iselectrically coupled to drain 8104. The use of a specific doping isillustrative, but not limiting in scope. For example, an inversely dopeddevice will operate similarly provided that the polarities are reversed,as such, the simple diode 6502 would operate similarly if the region8108 was doped N+, the region 8114 was doped N, the region 8110 wasdoped P+ while the polarity of electrical conductors 8120 and 8122 werereversed from their present state. If the source 8112 and the drain 8104are electrically connected together, then the hybrid active electronicand optical circuit device 6502 acts a diode instead of a field effecttransistor.

FIG. 90 shows one embodiment of field-plated diode 9002 that differsfrom the embodiment of diode shown in FIG. 81 primarily by the additionof an additional electrical conductor 8124 that is electricallyconnected to the gate 8106. The field-plated diode 9002 free carriercharacteristics can be altered by applying a potential to the gate 8106via the electrical conductor. Light can therefore be modulated. The gate8106 can be configured as viewed from above in a similar manner as theembodiments of active optical waveguide devices shown in FIGS. 1-5, and9-49 by appropriately shaping the gate electrode. A large variety oftransistor/diode devices can therefore be utilized as the activeelectronic portion of one embodiment of the hybrid active electronic andoptical circuit by similarly slight modifications. For example, FIG. 91shows one embodiment of a MOSFET 9101 (and if the source and drain areelectrically connected, a MOSCAP). Note that the doping of region 8110is the only structural difference between FIGS. 90 and 91. Such devicesare within the intended scope of the present invention.

Optically, light is guided perpendicular to the plane of the taper inFIG. 81, in a loaded optical structure 8112. The structure of glass andpolysilicon shown is an example in which the hybrid active electronicand optical circuit 6502 create a higher mode index in the center of theloaded optical structure 8112, in order to ease lateral confinement ofthe light flowing within the waveguide defined by the loaded opticalstructure 8112. This represents one embodiment of a lower waveguide.There are a large variety of diodes and transistors that FIG. 81represents an illustration of the operation thereof.

IX. Photonic Band Gap Device

This section describes certain aspects of shallow photonic band gapdevices. Whereas traditional photonic band gap devices extendsubstantially through the entire vertical height of the waveguide, theshallow photonic band gap devices extend through some percentage of thewaveguide. The inclusion of the shallow photonic band structure altersthe effective mode index in those regions of the waveguide that arebelow the shallow photonic band gap compared to those portions of theregions of the waveguide that are not below the shallow photonic bandgap. Depending on the gradient of the effective mode index within thewaveguide, the shallow photonic band gap devices provide an efficientand affordable optical device. It is envisioned that the shallowphotonic band gap devices can be used as a hybrid active electronic andoptical circuit 6502 as described herein by applying metal to eitherwithin the shallow photonic band gap devices or outside of the shallowphotonic band gap devices, and applying a controllable electric currentto the shallow photonic band gap devices. By applying an electricvoltage to the shallow photonic band gap devices, the effective modeindex within the region of the waveguide that is positioned adjacent tothe metalized portion can be controlled.

The photonic band gap device 9010 of FIGS. 82 to 85 is used to controland direct the flow of light. FIG. 82 shows one embodiment of atwo-dimensional embodiment of a photonic band gap device 9010 includinga substrate 9012, a waveguide 9014, a coupling prism 9016, and aplurality of regions of photonic crystals 9022. The photonic band gapdevice 9010 may be fashioned as a one-dimensional device (one embodimentshown in FIG. 84), a two-dimensional device (one embodiment shown inFIG. 85), or a three-dimensional device (one embodiment shown in FIG.87). The substrate 9012 is optional, and may not be provided in certainembodiments. In most SOI configurations, however, it is envisioned thatthe substrate 9012 will exist. In those embodiments in which thesubstrate is not provided, the waveguide 9014 is designed withsufficient strength and rigidity to sustain the physical forces that thecircuit would normally be expected to encounter.

The photonic band gap device may using prisms, gratings, or other suchcoupling devices to input/output light to the waveguide. The couplinginjects light into, or removes light from within, the waveguide. Oneembodiment of coupling a fiber to a photonic band gap device involvesabutting a fiber directly in contact with a fact of the waveguide toallow light to travel directly from the fiber into the waveguide.

The waveguide 9014 may include one or more channels 9024 that providefor the closely guided passage of light. Therefore, as shown in FIG. 82,light is applied from an incident field 9030 through a coupling prism9016, and thereby flows through the waveguide as indicated by arrow 9032to be directed toward the channel 9024. The horn 9034, in addition tothe channel 9024, defines another region within the waveguide (inaddition to the channel) in which no regions of photonic crystals (i.e.no pillars 9020) exist and light of the wavelength associated with theregion of photonic crystals is free to propagate. The horn 9034 isconfigured with one or more ramping sides 9040, that direct light withinthe waveguide as shown by arrow 9032 through the horn portion 9034 intothe channel 9024 that has much lesser thickness than that of thecoupling prism 9016.

Another aspect of coupling involves how one directs the light into achannel formed in the waveguide. The horn 9034 (shown in FIGS. 82 and83) is used for this latter photonic band gap device coupling. Theregion of photonic crystals 9022 is shaped to define the horn 9034. Thefirst and second coupling aspects can be considered independently.Irrespective of how light is injected into or removed from thewaveguide, however, the horn like structure can be used to direct thelight that is within the waveguide into a channel.

In one embodiment of one-dimensional waveguide 9014 shown in FIG. 83,the two regions of photonic crystals 9022 are arranged on opposing sidesof the channel 9024. Each region of photonic crystals 9022 is arrangedas a series of regularly spaced pillars 9220 formed of a material havingsimilar dielectric constants. The dielectric constant of pillars 9220differs from the region of the waveguide surrounding that pillar. Theregion of photonic crystals 9022 extends across the entire waveguideexcept for the regions required for the horn 9034 and the channel 9024.The one-dimensional regions of photonic crystals 9022 may be viewed asgratings in which alternating planes of different propagation constant(i.e. resulting from a varied effective mode index) are provided acrosswhich light traversing the waveguide passes.

In the embodiment of two-dimensional configuration shown in FIGS. 82 and83, the waveguide 9014 is formed with photonic crystals defines by theplurality of shallow pillars 9020 that do not extend through thevertical height of the waveguide 9014. The cross sectional shape of theshallow pillars is applied to the region under pillars. Photoniccrystals are defined by, and include, the pillars in the photonic bandgap device as well as the region underneath the pillars in which thedielectric constant of the material is varied by the pillars. Thepillars 9020 are arranged to define one or more regions of photoniccrystals 9022, and the spatial density of the pillars 9020 and theassociated projected photonic crystals within the region of photoniccrystals 9022 is sufficient to limit the passage of certain wavelengthsof light through each of the region of photonic crystals 9022. Thepillars 9020 in different embodiments of the photonic band gap device9010 may be left empty or filled with certain materials to allow for avariation in the propagation constant or effective index of the materialoutside of the photonic crystals 9022 compared to the material withineach one of the photonic crystals. The pillars 9020 may be formed byactual machining (such as removal of the material within the region ofphotonic crystals considered to form the pillar) or some other techniqueto alter the dielectric constant of the material within the pillarcompared with the material outside of the pillar. The pillars may beentirely physically formed or partially physically formed and partiallyprojected or entirely projected.

One embodiment of three-dimensional waveguide 9014 is shown in FIG. 87,and in top view in FIG. 85. The three-dimensional waveguide is formedfrom a plurality of alternating layers 9602, 9604, and 9606 that aresecured to one another. Shallow pillars 9610 are provided one of thealternating layers 9602 that alter the dielectric constant of a photoniccrystal formed by the shallow pillars 9610. From above, the shallowpillars 9602 are formed in an array configuration similar to as shown inFIG. 86. The layer 9604 positioned above layer 9602 includes anotherarray of shallow pillars 9610 that produce an array of photonic crystals9612 in layer 9604 similar as described above relative to the array ofshallow pillars 9610 in layer 9602. This staggering occurs in a planerfashion as viewed from above. The staggering of the shallow pillarsenhances the structural rigidity of the three-dimensional photonic bandgap device. The array of shallow pillars 9610 in each layer 9602, 9604,9606 is staggered relative to the array of shallow pillars in therespective layer above and below that layer. This staggering of thepillars 9602, 9604 provides for structural rigidity using a honeycomblike structure. Each layer is formed using regularly alternatingdielectric patterns between the pillars, and the material between thepillars. The material of each layer 9602, 9604, 9606 may be individuallyselected based upon its dielectric characteristics to provide a varietyof operations.

The waveguide in the photonic band gap device is mounted to thesubstrate. The substrate provides protection, rigidity, and support forthe waveguide in this embodiment. However, in other embodiments, nosubstrate is provided. In effect, the waveguide becomes a freestandingstructure. Therefore, any waveguide configuration that provides foreither free standing waveguides or waveguides mounted to, or affixed to,some sort of substrate is within the intended scope of the presentinvention.

The different embodiment of photonic band gap devices of the presentinvention may be fashioned as either active or passive devices. Passivephotonic band gap devices are considered to be those photonic band gapdevices that do not have an input (e.g., a voltage, current, optical, orany other signal) that controls the operation of the photonic band gapdevice. There are multiple embodiments of traditional photonic band gapdevices described herein that are within the scope of the presentinvention.

FIG. 83 shows one embodiment of passive photonic band gap device(referred to as a shallow passive photonic band gap device 9010) whoseregion of photonic crystals is delineated by shallow pillars which donot extend through the entire vertical height of the waveguide. In oneembodiment, the shallow passive pillars extend from the upper surfacefor a height h, but do not extend fully through the waveguide. Each oneof the shallow passive pillars 9220 can be biased to control therelative dielectric constants of those areas of waveguide material setforth under the shallow passive pillars. In certain embodiments ofshallow passive photonic band gap devices, the pillars are formed aswells, recesses, or indentations in the upper surface of the waveguide.FIG. 85 shows a top view of one embodiment of circular recesses thatdefine the shape of the pillars. The pillars can also be defined by thesquare, rectangular, or some other regularly repeated shape, as opposedto circular holes.

If the holes of the shallow passive pillars are not filled (andtherefore may be considered to be filled with air) the structure whichincludes the holes is not as structurally sound as solid waveguidedevices. Since the holes or gratings in the traditional photonic bandgap device extend vertically through the entire waveguide, the shallowpassive photonic band gap structure is structurally considerablystronger than the traditional photonic band gap device.

Once the voids are formed, they can be filled with some other material.In one embodiment, the hole can be filled with some photo resistantglass, metal, etc., and the uneven surface of the glass provided by thedeposition process is polished so the upper surface of the waveguide islevel again. This results in a photonic band gap device formed as asolid slab (without shallow pillars filled with air). The structure ofthis photonic bend gap device is almost as strong as the originalwaveguide before the shallow pillars were formed.

The shallow passive photonic band gap device 9010 is configured with anarray of wells or recesses that are formed which, for example, preventcertain colors of light from propagating at the location of the wells inthe shallow passive photonic band gap device 9010. The wells or recessesarea referred to as “shallow passive pillars”. The defects include themissing shallow passive pillars, rows of pillars, or gratings. Themissing shallow pillars can be formed by not providing any shallowpillars, or alternatively filling shallow pillars with a material thatshares the dielectric constant with the remainder of the waveguide. Anaspect ration of rod-shaped region of altered propagation constant thatextends below the shallow passive pillars is defined by theconfiguration of the shallow passive pillars (the aspect ratio ischaracterized by the height of the geometry divided by the diameter ofthe circle) and/or the state of the gate electrodes as discussed above.The present embodiment of shallow passive pillars may be drilled usinglithography techniques to provide approximately a 1:1 aspect ratio. Theaspect ratio is achievable and can be performed by most semiconductorfabs to provide this type of fabrication.

The contrast of the refractive index of the material in the shallowpassive pillars compared to the material in the remainder of thewaveguide is large, which is typical for shallow passive photonic bandgap devices (for example, the refractive index between silicon and airis on the order of index of 3.5). When the contrast of the refractiveindex is large, certain wavelengths of light are not allowed topropagate inside this material. If a light of such a wavelength (colors)were allowed to propagate in the medium, the light would be reflected.Such light can be diffracted by contacting regions of alteredpropagation constant (effective index) produced by the waveguidesshallow passive pillars extending into the waveguide.

Providing that the regions of altered propagation constant formed by theshallow passive pillars are formed in a funneling configuration, thenthe light of the appropriate wavelength is funneled into the channel.Light is guided essentially by the ramped walls. This process only worksover a certain range of colors. Certain colors (wavelengths) of lightscatter in such a way that that colors get reflected back out from thephotonic band gap device.

In photonic band gap devices, certain wavelengths of color are allowedto travel undeflected through the regions of altered propagationconstant within the photonic band gap device. The selection of lightthat passes through the regions of altered propagation constant definedin the waveguide beneath the shallow passive pillars are characterizedby Maxwell's equation. When the equation is solved, the certain colorswhich are allowed to propagate through the regions of alteredpropagation constant associated with each shallow passive pillar can bedetermined. The size of the shallow passive pillars are thus designed toact as a filter to restrict/pass certain wavelengths of light thatcorrespond to certain set of colors of interest. If a row or couple ofrows of these shallow passive pillars were deleted, then light couldtravel within the channel.

The channels between the regions of the shallow passive pillars 9220 areconfigured to be on the order of λ/2. The precise dimension depends onthe index contrast and all kinds of other things, but say that its ofthe order of 500 nm. It may be challenging to focus a light beam, so theefficiency of actually sending a light beam from some external sourceinto this channel is reduced. Much of the light hits the side walls, andreflects back. Only the part of the beam that is near a particularregion will go through. However, the horn takes a very broad beam oflight and slowly focuses it into the channel to get a very high couplinginto the channel. There are multiple embodiments of couplers including aprism, a grating, a butt coupling, and tapers.

Almost all of the light that enters a channel 9024 formed in a passivephotonic band gap device will exit the channel. The light passingthrough the channel appears as a little wire of light traveling alongthe channel. There will be some limited scattering and losses providedby the channel which means that the photonic crystals produced by thesepillars do not perfectly reflect light but instead the photonic crystalsscatter some negligible amount of light. Practically, the photoniccrystals defined by the pillars can be considered to be perfectly smoothand fully reflecting, and based upon the shape of the array of photoniccrystals, virtually all of the light is kept in the channel.

One embodiment of shallow passive photonic band gap device that isconfigured as a one-dimensional device, taken in perspective view, isshown as 9200 in FIG. 88. This embodiment includes a grating structureformed by a plurality of longitudinally extending lower lands 9202alternating with a plurality of longitudinally extending raised lands9204. The grating may be considered as a one dimensional version of theshallow pillars 9220 shown in FIG. 83. In the grating, light travellingin the waveguide passes through regions of altered propagation constantdefined by the areas under the pillars as the light flows through thewaveguide. The pillars can extend a variety of distances across thewidth of the waveguide. For example, the pillars can form the region ofphotonic crystals shown in FIG. 83.

The photonic band gap device can be configured in a one dimensionalconfiguration, a two dimensional configuration, and a three dimensionalconfiguration. One embodiment of one dimensional configuration of thephotonic band gap device is formed as a grating as shown in FIGS. 88 and89. Gratings have been disclosed herein in a variety of embodiments ofintegrated photonic/electronic circuits, it is envisioned that the termmay be applied to surface gratings or gratings. FIG. 88 shows a sideview of the grating shown in FIG. 88. The grating is shown by aplurality of alternating lower lands 9202 and a plurality of raisedlands 9204. The height of the lower lands 9202 defines a surface havinga thickness L1, and the raised land surface 9204, defines a surfacedefined by a thickness L2. Since L1 does not equal L2, the propagationconstant (or effective index) varies as indicated by n₁ and n₂. Thispropagation constant n₁ and n₂ extends throughout the entire regionunder each respective lower land 9202 and each raised land 9204.Therefore, a slight variation in the depth of the surface corrugation ofthe waveguide can provide a considerable difference in the effectiveindex (the propagation constant) throughout the waveguide. This is truefor one, two, or three dimensional shallow passive photonic band gapdevices. In this embodiment of photonic band gap device, it is desiredto use a single mode waveguide. The depth of the gratings can beprecisely controlled. The corregations of the gratings act to provide avariation of the effective mode index in the waveguide, as describedabove. As such, gratings are often used to diffract or reflect lightwithin a waveguide.

In one embodiment of grating, the corregations 2008 defined by the areaabove each lower land 9202 that is below the level of the raised land9204 and are filled only with air. In another embodiment, thecorregations are filled with, e.g., metal, glass, or other desiredmaterials that alter the propagation constant of the material inside thecorregation compared to the material outside the contour as indicated byfilled metal portion 2020 shown as the right-most corregation 2008. Thisstructure forms a one dimensional version of a shallow passive photonicband gap. Light travelling within the waveguide sees all thecorregations until the light sees the same index as the index of theband gap material. The depths of the corrugations 1008 can be controlledto effect the relative propagation constant of the material inside thewaveguide under the corrugations.

There can also be a three dimensional structure as shown in FIG. 86 madeby layering the two dimensional shallow passive photonic band gapstructures one on top of another. For each layer, each shallow passivepillar goes only part of the way through each respective layer. Thepillars in the three dimensional photonic band gap form what appears tobe a honeycomb structure. It is desired to vertically stagger thelocations of the shallow passive photonic band gap device so thestructurally weakest location of each layer is staggered to enhance therigidity of the photonic band gap device in each one of the threedimension. Another shallow passive pillar goes part of the way throughthe second layer. Since any shallow passive pillars do not extend allthe way through its waveguide, and since each shallow passive waveguidein certain embodiments is filled with a material such as metal, glass,etc., the resulting three dimensional photonic band gap device can beconstructed to be structurally sound. The device is scalable sincemultiple layers can be provided to increase the depth of the structure.

Complex light paths can be provided by light passing through thedifferent channels or paths. In one-dimensional shallow passive photonicband gap devices, the channels can be curved within zero or one plane.In two-dimensional shallow passive photonic band gap devices, thechannels can be curved within zero, one, or two planes. The resultingregions of shallow passive photonic crystals and channels can beconfigured in three dimensional shallow passive photonic band gapdevices to provide complex routes. In adjacent layers, light can be madeto turn off and be directed from one level to another level. Somecomplex structures can be built to provide complex light motion.

In some embodiments of photonic band gap devices, the light travellingthrough the channel is very tightly confined within the channel. Incertain cases, the light will not be that tightly confined depending onthe configuration and dimensions of the channel and the waveguide. Thelight will actually “spread out” perhaps to a width of three or four orfive lattices. The light will still be guided, but will not be confinedas precisely.

X. Simulation Program for Hybrid Active Electronic and Optical Circuits

FIG. 89 shows one embodiment of simulation program foroptical/electronics circuits 8200. Simulation is vital for both complexelectronic circuits and complex optical circuits since actuallyfabricating such circuits is extremely expensive and trial and error isprohibitively costly. The simulation program for optical/electroniccircuits 8200 includes an Electronic Design and Automation Tool (EDA)portion 8202 and an optical simulation design tool portion 8204. The EDAportion 8202 is used to simulate and design the operation of electronicdevices and circuits. The optical simulation design tool portion 8204 isused to design and simulate the operation of optical devices andcircuits. The EDA portion and the optical simulation design toolportions largely relies upon computer-based process, device, and circuitmodeling programs.

In the embodiment shown in FIG. 89, the EDA portion 8202 includes alayout portion 8206, a process simulation portion 8208, a devicesimulation portion 8210, a circuit simulation portion 8212, and aparasitic extraction portion 8214. These electronic portions areintended to be illustrative in nature, but not limiting in scope. Thespecific tools that are included in the EDA portion 8202 are a designchoice. Any suitable one or more computer program or electronicsimulation engine may be included in the EDA portion 8202, and remainwithin the scope of the present invention. Similarly, the embodiment ofoptical simulation design tool portion 8204 includes a gratings/DOEportion 8222, a finite different time domain (FDTD) portion 8220, a thinfilm portion 8224, a raytracing portion 8226, and a beam propagationmethod portion 8228. These optical portions are intended to beillustrative in nature, but not limiting in scope. The specific toolsthat are included in the optical simulation design tool portion 8204 area design choice. Any suitable one or more computer program or electronicsimulation engine may be included in the optical simulation design toolportion 8204, and remain within the scope of the present invention.

The EDA portion 8202 is commonly used in the semiconductor industry. Itis possible to use such EDA tools to design very complex electronicintegrated circuits on a computer. All circuit design from functionaldescription to circuit layout to circuit analysis can be performed basedon detailed modeling of actual transistors modeled from topology dopantprofiles generated by “virtual” process simulators, and semiconductordevice physics simulators.

Similarly, many optical tools exist to compute waveguide properties fora given topology, material, and index profile. The embodiment of FIG. 89specifically ties the two “separate” computational engines in whichoutput from the EDA portion 8202 are fed into optical simulation designtool portion 8204 to predict optical behavior.

For example, detailed topology, dopant profile and index profile can begenerated for passive SOI waveguide structures and thus can be fed intothe optical simulation design tool portion 8204 to be used to modeloptical passives. In order to model active opto-electronic devices, adevice physics simulator is also used to compute free carrierconcentration in Si as a function of voltage applied to vacuumelectrodes. This time dependent and space dependent concentration (andtherefore the ability to derive effective mode index) is fed into, forexample, PDTD to produce spatial and temporal behavior of optical beams.This optical behavior can then be used to extract “top-level” opticalparameters such as phase, extraction, chirp, extinction, and/or othersuch parameters. It is emphasized that there are a wide variety ofelectronics engines and optical engines that may be utilized in the EDAportion 8202 and optical simulation portions.

While the principles of the invention have been described above inconnection with the specific apparatus and associated method, it is tobe clearly understood that this description is made only by way ofexample and not as a limitation on the scope of the invention.

1. A method for forming a hybrid active electronic and optical circuitusing a lithography mask, the hybrid active electronic and opticalcircuit comprising an active electronic device and at least one opticaldevice, both devices disposed at least in part in a singleSilicon-On-Insulator (SOI) wafer, the SOI wafer including an insulatorlayer and an upper silicon layer, the upper silicon layer including atleast one component of the active electronic device and at least onecomponent of the optical device, the method comprising projecting thelithography mask onto the SOI waver in order to simultaneously patternthe component of the active electronic device and the component of theoptical device on the SOI wafer.
 2. The method of claim 1, whereinaltering an electric voltage level applied to the active electronicdevice effects the free carrier distribution in a region of the opticaldevice, and thereby changes the effective mode index of the region ofthe optical device.
 3. The method of claim 1, wherein the optical deviceis an active optical device includes an active optical device.
 4. Themethod of claim 1, wherein the optical device is includes a passiveoptical device.
 5. The method of claim 1, wherein the optical device isa focusing mirror.
 6. The method of claim 1, wherein the optical deviceis an input/output coupler that couples light into a waveguide.
 7. Themethod of claim 1, wherein the optical device is a Fabry-Perot cavity.8. The method of claim 1, wherein the optical device is a wavelengthdivision multiplexer modulator.
 9. The method of claim 1, wherein theoptical device is an evanescent coupler.
 10. The method of claim 1,wherein the optical device is a diode.
 11. The method of claim 1,wherein the optical device is a transistor.
 12. The method of claim 1,further comprising etching portions of the hybrid active electronic andoptical circuit from a surface of the SOI wafer utilizing thelithography mask.
 13. The method of claim 1, further comprisingdepositing materials on portions of the hybrid active electronic andoptical circuit to form a surface of the SOI wafer utilizing thelithography mask.
 14. The method of claim 1, wherein the optical deviceincludes one from the group of a p-n device, a field plated device, aSchottky device, a MOSCAP, and a MOSFET.
 15. A method for forming ahybrid active electronic and optical circuit using a lithography mask,the hybrid active electronic and optical circuit comprising an activeelectronic device and at least one optical device, both devices disposedat least in part in a single wafer, the wafer including an insulatorlayer and an upper silicon layer, the upper silicon layer including atleast one component of the active electronic device and at least onecomponent of the optical device, the method comprising projecting thelithography mask onto the wafer in order to simultaneously pattern thecomponent of the active electronic device and the component of theoptical device on the wafer.
 16. The method of claim 15, wherein thewafer is a silicon-on-sapphire wafer.